/* $FreeBSD: head/sys/dev/isp/DriverManual.txt 298955 2016-05-03 03:41:25Z pfg $ */ Driver Theory of Operation Manual 1. Introduction This is a short text document that will describe the background, goals for, and current theory of operation for the joint Fibre Channel/SCSI HBA driver for QLogic hardware. Because this driver is an ongoing project, do not expect this manual to remain entirely up to date. Like a lot of software engineering, the ultimate documentation is the driver source. However, this manual should serve as a solid basis for attempting to understand where the driver started and what is trying to be accomplished with the current source. The reader is expected to understand the basics of SCSI and Fibre Channel and to be familiar with the range of platforms that Solaris, Linux and the variant "BSD" Open Source systems are available on. A glossary and a few references will be placed at the end of the document. There will be references to functions and structures within the body of this document. These can be easily found within the source using editor tags or grep. There will be few code examples here as the code already exists where the reader can easily find it. 2. A Brief History for this Driver This driver originally started as part of work funded by NASA Ames Research Center's Numerical Aerodynamic Simulation center ("NAS" for short) for the QLogic PCI 1020 and 1040 SCSI Host Adapters as part of my work at porting the NetBSD Operating System to the Alpha architectures (specifically the AlphaServer 8200 and 8400 platforms). In short, it started just as simple single SCSI HBA driver for just the purpose of running off a SCSI disk. This work took place starting in January, 1997. Because the first implementation was for NetBSD, which runs on a very large number of platforms, and because NetBSD supported both systems with SBus cards (e.g., Sun SPARC systems) as well as systems with PCI cards, and because the QLogic SCSI cards came in both SBus and PCI versions, the initial implementation followed the very thoughtful NetBSD design tenet of splitting drivers into what are called MI (for Machine Independent) and MD (Machine Dependent) portions. The original design therefore was from the premise that the driver would drive both SBus and PCI card variants. These busses are similar but have quite different constraints, and while the QLogic SBus and PCI cards are very similar, there are some significant differences. After this initial goal had been met, there began to be some talk about looking into implementing Fibre Channel mass storage at NAS. At this time the QLogic 2100 FC/AL HBA was about to become available. After looking at the way it was designed I concluded that it was so darned close to being just like the SCSI HBAs that it would be insane to *not* leverage off of the existing driver. So, we ended up with a driver for NetBSD that drove PCI and SBus SCSI cards, and now also drove the QLogic 2100 FC-AL HBA. After this, ports to non-NetBSD platforms became interesting as well. This took the driver out of the interest with NAS and into interested support from a number of other places. Since the original NetBSD development, the driver has been ported to FreeBSD, OpenBSD, Linux, Solaris, and two proprietary systems. Following from the original MI/MD design of NetBSD, a rather successful attempt has been made to keep the Operating System Platform differences segregated and to a minimum. Along the way, support for the 2200 as well as full fabric and target mode support has been added, and 2300 support as well as an FC-IP stack are planned. 3. Driver Design Goals The driver has not started out as one normally would do such an effort. Normally you design via top-down methodologies and set an initial goal and meet it. This driver has had a design goal that changes from almost the very first. This has been an extremely peculiar, if not risque, experience. As a consequence, this section of this document contains a bit of "reconstruction after the fact" in that the design goals are as I perceive them to be now- not necessarily what they started as. The primary design goal now is to have a driver that can run both the SCSI and Fibre Channel SCSI prototocols on multiple OS platforms with as little OS platform support code as possible. The intended support targets for SCSI HBAs is to support the single and dual channel PCI Ultra2 and PCI Ultra3 cards as well as the older PCI Ultra single channel cards and SBus cards. The intended support targets for Fibre Channel HBAs is the 2100, 2200 and 2300 PCI cards. Fibre Channel support should include complete fabric and public loop as well as private loop and private loop, direct-attach topologies. FC-IP support is also a goal. For both SCSI and Fibre Channel, simultaneous target/initiator mode support is a goal. Pure, raw, performance is not a primary goal of this design. This design, because it has a tremendous amount of code common across multiple platforms, will undoubtedly never be able to beat the performance of a driver that is specifically designed for a single platform and a single card. However, it is a good strong secondary goal to make the performance penalties in this design as small as possible. Another primary aim, which almost need not be stated, is that the implementation of platform differences must not clutter up the common code with platform specific defines. Instead, some reasonable layering semantics are defined such that platform specifics can be kept in the platform specific code. 4. QLogic Hardware Architecture In order to make the design of this driver more intelligible, some description of the Qlogic hardware architecture is in order. This will not be an exhaustive description of how this card works, but will note enough of the important features so that the driver design is hopefully clearer. 4.1 Basic QLogic hardware The QLogic HBA cards all contain a tiny 16-bit RISC-like processor and varying sizes of SRAM. Each card contains a Bus Interface Unit (BIU) as appropriate for the host bus (SBus or PCI). The BIUs allow access to a set of dual-ranked 16 bit incoming and outgoing mailbox registers as well as access to control registers that control the RISC or access other portions of the card (e.g., Flash BIOS). The term 'dual-ranked' means that at the same host visible address if you write a mailbox register, that is a write to an (incoming, to the HBA) mailbox register, while a read to the same address reads another (outgoing, to the HBA) mailbox register with completely different data. Each HBA also then has core and auxiliary logic which either is used to interface to a SCSI bus (or to external bus drivers that connect to a SCSI bus), or to connect to a Fibre Channel bus. 4.2 Basic Control Interface There are two principle I/O control mechanisms by which the driver communicates with and controls the QLogic HBA. The first mechanism is to use the incoming mailbox registers to interrupt and issue commands to the RISC processor (with results usually, but not always, ending up in the ougtoing mailbox registers). The second mechanism is to establish, via mailbox commands, circular request and response queues in system memory that are then shared between the QLogic and the driver. The request queue is used to queue requests (e.g., I/O requests) for the QLogic HBA's RISC engine to copy into the HBA memory and process. The result queue is used by the QLogic HBA's RISC engine to place results of requests read from the request queue, as well as to place notification of asynchronous events (e.g., incoming commands in target mode). To give a bit more precise scale to the preceding description, the QLogic HBA has 8 dual-ranked 16 bit mailbox registers, mostly for out-of-band control purposes. The QLogic HBA then utilizes a circular request queue of 64 byte fixed size Queue Entries to receive normal initiator mode I/O commands (or continue target mode requests). The request queue may be up to 256 elements for the QLogic 1020 and 1040 chipsets, but may be quite larger for the QLogic 12X0/12160 SCSI and QLogic 2X00 Fibre Channel chipsets. In addition to synchronously initiated usage of mailbox commands by the host system, the QLogic may also deliver asynchronous notifications solely in outgoing mailbox registers. These asynchronous notifications in mailboxes may be things like notification of SCSI Bus resets, or that the Fabric Name server has sent a change notification, or even that a specific I/O command completed without error (this is called 'Fast Posting' and saves the QLogic HBA from having to write a response queue entry). The QLogic HBA is an interrupting card, and when servicing an interrupt you really only have to check for either a mailbox interrupt or an interrupt notification that the response queue has an entry to be dequeued. 4.3 Fibre Channel SCSI out of SCSI QLogic took the approach in introducing the 2X00 cards to just treat FC-AL as a 'fat' SCSI bus (a SCSI bus with more than 15 targets). All of the things that you really need to do with Fibre Channel with respect to providing FC-4 services on top of a Class 3 connection are performed by the RISC engine on the QLogic card itself. This means that from an HBA driver point of view, very little needs to change that would distinguish addressing a Fibre Channel disk from addressing a plain old SCSI disk. However, in the details it's not *quite* that simple. For example, in order to manage Fabric Connections, the HBA driver has to do explicit binding of entities it's queried from the name server to specific 'target' ids (targets, in this case, being a virtual entity). Still- the HBA firmware does really nearly all of the tedious management of Fibre Channel login state. The corollary to this sometimes is the lack of ability to say why a particular login connection to a Fibre Channel disk is not working well. There are clear limits with the QLogic card in managing fabric devices. The QLogic manages local loop devices (LoopID or Target 0..126) itself, but for the management of fabric devices, it has an absolute limit of 253 simultaneous connections (256 entries less 3 reserved entries). 5. Driver Architecture 5.1 Driver Assumptions The first basic assumption for this driver is that the requirements for a SCSI HBA driver for any system is that of a 2 or 3 layer model where there are SCSI target device drivers (drivers which drive SCSI disks, SCSI tapes, and so on), possibly a middle services layer, and a bottom layer that manages the transport of SCSI CDB's out a SCSI bus (or across Fibre Channel) to a SCSI device. It's assumed that each SCSI command is a separate structure (or pointer to a structure) that contains the SCSI CDB and a place to store SCSI Status and SCSI Sense Data. This turns out to be a pretty good assumption. All of the Open Source systems (*BSD and Linux) and most of the proprietary systems have this kind of structure. This has been the way to manage SCSI subsystems for at least ten years. There are some additional basic assumptions that this driver makes- primarily in the arena of basic simple services like memory zeroing, memory copying, delay, sleep, microtime functions. It doesn't assume much more than this. 5.2 Overall Driver Architecture The driver is split into a core (machine independent) module and platform and bus specific outer modules (machine dependent). The core code (in the files isp.c, isp_inline.h, ispvar.h, ispreg.h and ispmbox.h) handles: + Chipset recognition and reset and firmware download (isp_reset) + Board Initialization (isp_init) + First level interrupt handling (response retrieval) (isp_intr) + A SCSI command queueing entry point (isp_start) + A set of control services accessed either via local requirements within the core module or via an externally visible control entry point (isp_control). The platform/bus specific modules (and definitions) depend on each platform, and they provide both definitions and functions for the core module's use. Generally a platform module set is split into a bus dependent module (where configuration is begun from and bus specific support functions reside) and relatively thin platform specific layer which serves as the interconnect with the rest of this platform's SCSI subsystem. For ease of bus specific access issues, a centralized soft state structure is maintained for each HBA instance (struct ispsoftc). This soft state structure contains a machine/bus dependent vector (mdvec) for functions that read and write hardware registers, set up DMA for the request/response queues and fibre channel scratch area, set up and tear down DMA mappings for a SCSI command, provide a pointer to firmware to load, and other minor things. The machine dependent outer module must provide functional entry points for the core module: + A SCSI command completion handoff point (isp_done) + An asynchronous event handler (isp_async) + A logging/printing function (isp_prt) The machine dependent outer module code must also provide a set of abstracting definitions which is what the core module utilizes heavily to do its job. These are discussed in detail in the comments in the file ispvar.h, but to give a sense of the range of what is required, let's illustrate two basic classes of these defines. The first class are "structure definition/access" class. An example of these would be: XS_T Platform SCSI transaction type (i.e., command for HBA) .. XS_TGT(xs) gets the target from an XS_T .. XS_TAG_TYPE(xs) which type of tag to use .. The second class are 'functional' class definitions. Some examples of this class are: MEMZERO(dst, src) platform zeroing function .. MBOX_WAIT_COMPLETE(struct ispsoftc *) wait for mailbox cmd to be done Note that the former is likely to be simple replacement with bzero or memset on most systems, while the latter could be quite complex. This soft state structure also contains different parameter information based upon whether this is a SCSI HBA or a Fibre Channel HBA (which is filled in by the code module). In order to clear up what is undoubtedly a seeming confusion of interconnects, a description of the typical flow of code that performs boards initialization and command transactions may help. 5.3 Initialization Code Flow Typically a bus specific module for a platform (e.g., one that wants to configure a PCI card) is entered via that platform's configuration methods. If this module recognizes a card and can utilize or construct the space for the HBA instance softc, it does so, and initializes the machine dependent vector as well as any other platform specific information that can be hidden in or associated with this structure. Configuration at this point usually involves mapping in board registers and registering an interrupt. It's quite possible that the core module's isp_intr function is adequate to be the interrupt entry point, but often it's more useful have a bus specific wrapper module that calls isp_intr. After mapping and interrupt registry is done, isp_reset is called. Part of the isp_reset call may cause callbacks out to the bus dependent module to perform allocation and/or mapping of Request and Response queues (as well as a Fibre Channel scratch area if this is a Fibre Channel HBA). The reason this is considered 'bus dependent' is that only the bus dependent module may have the information that says how one could perform I/O mapping and dependent (e.g., on a Solaris system) on the Request and Response queues. Another callback can enable the *use* of interrupts should this platform be able to finish configuration in interrupt driven mode. If isp_reset is successful at resetting the QLogic chipset and downloading new firmware (if available) and setting it running, isp_init is called. If isp_init is successful in doing initial board setups (including reading NVRAM from the QLogic card), then this bus specicic module will call the platform dependent module that takes the appropriate steps to 'register' this HBA with this platform's SCSI subsystem. Examining either the OpenBSD or the NetBSD isp_pci.c or isp_sbus.c files may assist the reader here in clarifying some of this. 5.4 Initiator Mode Command Code Flow A successful execution of isp_init will lead to the driver 'registering' itself with this platform's SCSI subsystem. One assumed action for this is the registry of a function that the SCSI subsystem for this platform will call when it has a SCSI command to run. The platform specific module function that receives this will do whatever it needs to to prepare this command for execution in the core module. This sounds vague, but it's also very flexible. In principle, this could be a complete marshalling/demarshalling of this platform's SCSI command structure (should it be impossible to represent in an XS_T). In addition, this function can also block commands from running (if, e.g., Fibre Channel loop state would preclude successful starting of the command). When it's ready to do so, the function isp_start is called with this command. This core module tries to allocate request queue space for this command. It also calls through the machine dependent vector function to make sure any DMA mapping for this command is done. Now, DMA mapping here is possibly a misnomer, as more than just DMA mapping can be done in this bus dependent function. This is also the place where any endian byte-swizzling will be done. At any rate, this function is called last because the process of establishing DMA addresses for any command may in fact consume more Request Queue entries than there are currently available. If the mapping and other functions are successful, the QLogic mailbox inbox pointer register is updated to indicate to the QLogic that it has a new request to read. If this function is unsuccessful, policy as to what to do at this point is left to the machine dependent platform function which called isp_start. In some platforms, temporary resource shortages can be handled by the main SCSI subsystem. In other platforms, the machine dependent code has to handle this. In order to keep track of commands that are in progress, the soft state structure contains an array of 'handles' that are associated with each active command. When you send a command to the QLogic firmware, a portion of the Request Queue entry can contain a non-zero handle identifier so that at a later point in time in reading either a Response Queue entry or from a Fast Posting mailbox completion interrupt, you can take this handle to find the command you were waiting on. It should be noted that this is probably one of the most dangerous areas of this driver. Corrupted handles will lead to system panics. At some later point in time an interrupt will occur. Eventually, isp_intr will be called. This core module will determine what the cause of the interrupt is, and if it is for a completing command. That is, it'll determine the handle and fetch the pointer to the command out of storage within the soft state structure. Skipping over a lot of details, the machine dependent code supplied function isp_done is called with the pointer to the completing command. This would then be the glue layer that informs the SCSI subsystem for this platform that a command is complete. 5.5 Asynchronous Events Interrupts occur for events other than commands (mailbox or request queue started commands) completing. These are called Asynchronous Mailbox interrupts. When some external event causes the SCSI bus to be reset, or when a Fibre Channel loop changes state (e.g., a LIP is observed), this generates such an asynchronous event. Each platform module has to provide an isp_async entry point that will handle a set of these. This isp_async entry point also handles things which aren't properly async events but are simply natural outgrowths of code flow for another core function (see discussion on fabric device management below). 5.6 Target Mode Code Flow This section could use a lot of expansion, but this covers the basics. The QLogic cards, when operating in target mode, follow a code flow that is essentially the inverse of that for intiator mode describe above. In this scenario, an interrupt occurs, and present on the Response Queue is a queue entry element defining a new command arriving from an initiator. This is passed to possibly external target mode handler. This driver provides some handling for this in a core module, but also leaves things open enough that a completely different target mode handler may accept this incoming queue entry. The external target mode handler then turns around forms up a response to this 'response' that just arrived which is then placed on the Request Queue and handled very much like an initiator mode command (i.e., calling the bus dependent DMA mapping function). If this entry completes the command, no more need occur. But often this handles only part of the requested command, so the QLogic firmware will rewrite the response to the initial 'response' again onto the Response Queue, whereupon the target mode handler will respond to that, and so on until the command is completely handled. Because almost no platform provides basic SCSI Subsystem target mode support, this design has been left extremely open ended, and as such it's a bit hard to describe in more detail than this. 5.7 Locking Assumptions The observant reader by now is likely to have asked the question, "but what about locking? Or interrupt masking" by now. The basic assumption about this is that the core module does not know anything directly about locking or interrupt masking. It may assume that upon entry (e.g., via isp_start, isp_control, isp_intr) that appropriate locking and interrupt masking has been done. The platform dependent code may also therefore assume that if it is called (e.g., isp_done or isp_async) that any locking or masking that was in place upon the entry to the core module is still there. It is up to the platform dependent code to worry about avoiding any lock nesting issues. As an example of this, the Linux implementation simply queues up commands completed via the callout to isp_done, which it then pushes out to the SCSI subsystem after a return from it's calling isp_intr is executed (and locks dropped appropriately, as well as avoidance of deep interrupt stacks). Recent changes in the design have now eased what had been an original requirement that the while in the core module no locks or interrupt masking could be dropped. It's now up to each platform to figure out how to implement this. This is principally used in the execution of mailbox commands (which are principally used for Loop and Fabric management via the isp_control function). 5.8 SCSI Specifics The driver core or platform dependent architecture issues that are specific to SCSI are few. There is a basic assumption that the QLogic firmware supported Automatic Request sense will work- there is no particular provision for disabling it's usage on a per-command basis. 5.9 Fibre Channel Specifics Fibre Channel presents an interesting challenge here. The QLogic firmware architecture for dealing with Fibre Channel as just a 'fat' SCSI bus is fine on the face of it, but there are some subtle and not so subtle problems here. 5.9.1 Firmware State Part of the initialization (isp_init) for Fibre Channel HBAs involves sending a command (Initialize Control Block) that establishes Node and Port WWNs as well as topology preferences. After this occurs, the QLogic firmware tries to traverese through serveral states: FW_CONFIG_WAIT FW_WAIT_AL_PA FW_WAIT_LOGIN FW_READY FW_LOSS_OF_SYNC FW_ERROR FW_REINIT FW_NON_PART It starts with FW_CONFIG_WAIT, attempts to get an AL_PA (if on an FC-AL loop instead of being connected as an N-port), waits to log into all FC-AL loop entities and then hopefully transitions to FW_READY state. Clearly, no command should be attempted prior to FW_READY state is achieved. The core internal function isp_fclink_test (reachable via isp_control with the ISPCTL_FCLINK_TEST function code). This function also determines connection topology (i.e., whether we're attached to a fabric or not). 5.9.2. Loop State Transitions- From Nil to Ready Once the firmware has transitioned to a ready state, then the state of the connection to either arbitrated loop or to a fabric has to be ascertained, and the identity of all loop members (and fabric members validated). This can be very complicated, and it isn't made easy in that the QLogic firmware manages PLOGI and PRLI to devices that are on a local loop, but it is the driver that must manage PLOGI/PRLI with devices on the fabric. In order to manage this state an eight level staging of current "Loop" (where "Loop" is taken to mean FC-AL or N- or F-port connections) states in the following ascending order: LOOP_NIL LOOP_LIP_RCVD LOOP_PDB_RCVD LOOP_SCANNING_FABRIC LOOP_FSCAN_DONE LOOP_SCANNING_LOOP LOOP_LSCAN_DONE LOOP_SYNCING_PDB LOOP_READY When the core code initializes the QLogic firmware, it sets the loop state to LOOP_NIL. The first 'LIP Received' asynchronous event sets state to LOOP_LIP_RCVD. This should be followed by a "Port Database Changed" asynchronous event which will set the state to LOOP_PDB_RCVD. Each of these states, when entered, causes an isp_async event call to the machine dependent layers with the ISPASYNC_CHANGE_NOTIFY code. After the state of LOOP_PDB_RCVD is reached, the internal core function isp_scan_fabric (reachable via isp_control(..ISPCTL_SCAN_FABRIC)) will, if the connection is to a fabric, use Simple Name Server mailbox mediated commands to dump the entire fabric contents. For each new entity, an isp_async event will be generated that says a Fabric device has arrived (ISPASYNC_FABRIC_DEV). The function that isp_async must perform in this step is to insert possibly remove devices that it wants to have the QLogic firmware log into (at LOOP_SYNCING_PDB state level)). After this has occurred, the state LOOP_FSCAN_DONE is set, and then the internal function isp_scan_loop (isp_control(...ISPCTL_SCAN_LOOP)) can be called which will then scan for any local (FC-AL) entries by asking for each possible local loop id the QLogic firmware for a Port Database entry. It's at this level some entries cached locally are purged or shifting loopids are managed (see section 5.9.4). The final step after this is to call the internal function isp_pdb_sync (isp_control(..ISPCTL_PDB_SYNC)). The purpose of this function is to then perform the PLOGI/PRLI functions for fabric devices. The next state entered after this is LOOP_READY, which means that the driver is ready to process commands to send to Fibre Channel devices. 5.9.3 Fibre Channel variants of Initiator Mode Code Flow The code flow in isp_start for Fibre Channel devices is the same as it is for SCSI devices, but with a notable exception. Maintained within the fibre channel specific portion of the driver soft state structure is a distillation of the existing population of both local loop and fabric devices. Because Loop IDs can shift on a local loop but we wish to retain a 'constant' Target ID (see 5.9.4), this is indexed directly via the Target ID for the command (XS_TGT(xs)). If there is a valid entry for this Target ID, the command is started (with the stored 'Loop ID'). If not the command is completed with the error that is just like a SCSI Selection Timeout error. This code is currently somewhat in transition. Some platforms to do firmware and loop state management (as described above) at this point. Other platforms manage this from the machine dependent layers. The important function to watch in this respect is isp_fc_runstate (in isp_inline.h). 5.9.4 "Target" in Fibre Channel is a fixed virtual construct Very few systems can cope with the notion that "Target" for a disk device can change while you're using it. But one of the properties of for arbitrated loop is that the physical bus address for a loop member (the AL_PA) can change depending on when and how things are inserted in the loop. To illustrate this, let's take an example. Let's say you start with a loop that has 5 disks in it. At boot time, the system will likely find them and see them in this order: disk# Loop ID Target ID disk0 0 0 disk1 1 1 disk2 2 2 disk3 3 3 disk4 4 4 The driver uses 'Loop ID' when it forms requests to send a comamnd to each disk. However, it reports to NetBSD that things exist as 'Target ID'. As you can see here, there is perfect correspondence between disk, Loop ID and Target ID. Let's say you add a new disk between disk2 and disk3 while things are running. You don't really often see this, but you *could* see this where the loop has to renegotiate, and you end up with: disk# Loop ID Target ID disk0 0 0 disk1 1 1 disk2 2 2 diskN 3 ? disk3 4 ? disk4 5 ? Clearly, you don't want disk3 and disk4's "Target ID" to change while you're running since currently mounted filesystems will get trashed. What the driver is supposed to do (this is the function of isp_scan_loop), is regenerate things such that the following then occurs: disk# Loop ID Target ID disk0 0 0 disk1 1 1 disk2 2 2 diskN 3 5 disk3 4 3 disk4 5 4 So, "Target" is a virtual entity that is maintained while you're running. 6. Glossary HBA - Host Bus Adapter SCSI - Small Computer 7. References Various URLs of interest: http://www.netbsd.org - NetBSD's Web Page http://www.openbsd.org - OpenBSD's Web Page http://www.freebsd.org - FreeBSD's Web Page http://www.t10.org - ANSI SCSI Commitee's Web Page (SCSI Specs) http://www.t11.org - NCITS Device Interface Web Page (Fibre Channel Specs)