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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/sparc/sbus_drivers.txt | 309 |
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diff --git a/Documentation/sparc/sbus_drivers.txt b/Documentation/sparc/sbus_drivers.txt deleted file mode 100644 index eb1e28a..0000000 --- a/Documentation/sparc/sbus_drivers.txt +++ /dev/null @@ -1,309 +0,0 @@ - - Writing SBUS Drivers - - David S. Miller (davem@redhat.com) - - The SBUS driver interfaces of the Linux kernel have been -revamped completely for 2.4.x for several reasons. Foremost were -performance and complexity concerns. This document details these -new interfaces and how they are used to write an SBUS device driver. - - SBUS drivers need to include <asm/sbus.h> to get access -to functions and structures described here. - - Probing and Detection - - Each SBUS device inside the machine is described by a -structure called "struct sbus_dev". Likewise, each SBUS bus -found in the system is described by a "struct sbus_bus". For -each SBUS bus, the devices underneath are hung in a tree-like -fashion off of the bus structure. - - The SBUS device structure contains enough information -for you to implement your device probing algorithm and obtain -the bits necessary to run your device. The most commonly -used members of this structure, and their typical usage, -will be detailed below. - - Here is a piece of skeleton code for performing a device -probe in an SBUS driver under Linux: - - static int __devinit mydevice_probe_one(struct sbus_dev *sdev) - { - struct mysdevice *mp = kzalloc(sizeof(*mp), GFP_KERNEL); - - if (!mp) - return -ENODEV; - - ... - dev_set_drvdata(&sdev->ofdev.dev, mp); - return 0; - ... - } - - static int __devinit mydevice_probe(struct of_device *dev, - const struct of_device_id *match) - { - struct sbus_dev *sdev = to_sbus_device(&dev->dev); - - return mydevice_probe_one(sdev); - } - - static int __devexit mydevice_remove(struct of_device *dev) - { - struct sbus_dev *sdev = to_sbus_device(&dev->dev); - struct mydevice *mp = dev_get_drvdata(&dev->dev); - - return mydevice_remove_one(sdev, mp); - } - - static struct of_device_id mydevice_match[] = { - { - .name = "mydevice", - }, - {}, - }; - - MODULE_DEVICE_TABLE(of, mydevice_match); - - static struct of_platform_driver mydevice_driver = { - .match_table = mydevice_match, - .probe = mydevice_probe, - .remove = __devexit_p(mydevice_remove), - .driver = { - .name = "mydevice", - }, - }; - - static int __init mydevice_init(void) - { - return of_register_driver(&mydevice_driver, &sbus_bus_type); - } - - static void __exit mydevice_exit(void) - { - of_unregister_driver(&mydevice_driver); - } - - module_init(mydevice_init); - module_exit(mydevice_exit); - - The mydevice_match table is a series of entries which -describes what SBUS devices your driver is meant for. In the -simplest case you specify a string for the 'name' field. Every -SBUS device with a 'name' property matching your string will -be passed one-by-one to your .probe method. - - You should store away your device private state structure -pointer in the drvdata area so that you can retrieve it later on -in your .remove method. - - Any memory allocated, registers mapped, IRQs registered, -etc. must be undone by your .remove method so that all resources -of your device are released by the time it returns. - - You should _NOT_ use the for_each_sbus(), for_each_sbusdev(), -and for_all_sbusdev() interfaces. They are deprecated, will be -removed, and no new driver should reference them ever. - - Mapping and Accessing I/O Registers - - Each SBUS device structure contains an array of descriptors -which describe each register set. We abuse struct resource for that. -They each correspond to the "reg" properties provided by the OBP firmware. - - Before you can access your device's registers you must map -them. And later if you wish to shutdown your driver (for module -unload or similar) you must unmap them. You must treat them as -a resource, which you allocate (map) before using and free up -(unmap) when you are done with it. - - The mapping information is stored in an opaque value -typed as an "unsigned long". This is the type of the return value -of the mapping interface, and the arguments to the unmapping -interface. Let's say you want to map the first set of registers. -Perhaps part of your driver software state structure looks like: - - struct mydevice { - unsigned long control_regs; - ... - struct sbus_dev *sdev; - ... - }; - - At initialization time you then use the sbus_ioremap -interface to map in your registers, like so: - - static void init_one_mydevice(struct sbus_dev *sdev) - { - struct mydevice *mp; - ... - - mp->control_regs = sbus_ioremap(&sdev->resource[0], 0, - CONTROL_REGS_SIZE, "mydevice regs"); - if (!mp->control_regs) { - /* Failure, cleanup and return. */ - } - } - - Second argument to sbus_ioremap is an offset for -cranky devices with broken OBP PROM. The sbus_ioremap uses only -a start address and flags from the resource structure. -Therefore it is possible to use the same resource to map -several sets of registers or even to fabricate a resource -structure if driver gets physical address from some private place. -This practice is discouraged though. Use whatever OBP PROM -provided to you. - - And here is how you might unmap these registers later at -driver shutdown or module unload time, using the sbus_iounmap -interface: - - static void mydevice_unmap_regs(struct mydevice *mp) - { - sbus_iounmap(mp->control_regs, CONTROL_REGS_SIZE); - } - - Finally, to actually access your registers there are 6 -interface routines at your disposal. Accesses are byte (8 bit), -word (16 bit), or longword (32 bit) sized. Here they are: - - u8 sbus_readb(unsigned long reg) /* read byte */ - u16 sbus_readw(unsigned long reg) /* read word */ - u32 sbus_readl(unsigned long reg) /* read longword */ - void sbus_writeb(u8 value, unsigned long reg) /* write byte */ - void sbus_writew(u16 value, unsigned long reg) /* write word */ - void sbus_writel(u32 value, unsigned long reg) /* write longword */ - - So, let's say your device has a control register of some sort -at offset zero. The following might implement resetting your device: - - #define CONTROL 0x00UL - - #define CONTROL_RESET 0x00000001 /* Reset hardware */ - - static void mydevice_reset(struct mydevice *mp) - { - sbus_writel(CONTROL_RESET, mp->regs + CONTROL); - } - - Or perhaps there is a data port register at an offset of -16 bytes which allows you to read bytes from a fifo in the device: - - #define DATA 0x10UL - - static u8 mydevice_get_byte(struct mydevice *mp) - { - return sbus_readb(mp->regs + DATA); - } - - It's pretty straightforward, and clueful readers may have -noticed that these interfaces mimick the PCI interfaces of the -Linux kernel. This was not by accident. - - WARNING: - - DO NOT try to treat these opaque register mapping - values as a memory mapped pointer to some structure - which you can dereference. - - It may be memory mapped, it may not be. In fact it - could be a physical address, or it could be the time - of day xor'd with 0xdeadbeef. :-) - - Whatever it is, it's an implementation detail. The - interface was done this way to shield the driver - author from such complexities. - - Doing DVMA - - SBUS devices can perform DMA transactions in a way similar -to PCI but dissimilar to ISA, e.g. DMA masters supply address. -In contrast to PCI, however, that address (a bus address) is -translated by IOMMU before a memory access is performed and therefore -it is virtual. Sun calls this procedure DVMA. - - Linux supports two styles of using SBUS DVMA: "consistent memory" -and "streaming DVMA". CPU view of consistent memory chunk is, well, -consistent with a view of a device. Think of it as an uncached memory. -Typically this way of doing DVMA is not very fast and drivers use it -mostly for control blocks or queues. On some CPUs we cannot flush or -invalidate individual pages or cache lines and doing explicit flushing -over ever little byte in every control block would be wasteful. - -Streaming DVMA is a preferred way to transfer large amounts of data. -This process works in the following way: -1. a CPU stops accessing a certain part of memory, - flushes its caches covering that memory; -2. a device does DVMA accesses, then posts an interrupt; -3. CPU invalidates its caches and starts to access the memory. - -A single streaming DVMA operation can touch several discontiguous -regions of a virtual bus address space. This is called a scatter-gather -DVMA. - -[TBD: Why do not we neither Solaris attempt to map disjoint pages -into a single virtual chunk with the help of IOMMU, so that non SG -DVMA masters would do SG? It'd be very helpful for RAID.] - - In order to perform a consistent DVMA a driver does something -like the following: - - char *mem; /* Address in the CPU space */ - u32 busa; /* Address in the SBus space */ - - mem = (char *) sbus_alloc_consistent(sdev, MYMEMSIZE, &busa); - - Then mem is used when CPU accesses this memory and u32 -is fed to the device so that it can do DVMA. This is typically -done with an sbus_writel() into some device register. - - Do not forget to free the DVMA resources once you are done: - - sbus_free_consistent(sdev, MYMEMSIZE, mem, busa); - - Streaming DVMA is more interesting. First you allocate some -memory suitable for it or pin down some user pages. Then it all works -like this: - - char *mem = argumen1; - unsigned int size = argument2; - u32 busa; /* Address in the SBus space */ - - *mem = 1; /* CPU can access */ - busa = sbus_map_single(sdev, mem, size); - if (busa == 0) ....... - - /* Tell the device to use busa here */ - /* CPU cannot access the memory without sbus_dma_sync_single() */ - - sbus_unmap_single(sdev, busa, size); - if (*mem == 0) .... /* CPU can access again */ - - It is possible to retain mappings and ask the device to -access data again and again without calling sbus_unmap_single. -However, CPU caches must be invalidated with sbus_dma_sync_single -before such access. - -[TBD but what about writeback caches here... do we have any?] - - There is an equivalent set of functions doing the same thing -only with several memory segments at once for devices capable of -scatter-gather transfers. Use the Source, Luke. - - Examples - - drivers/net/sunhme.c - This is a complicated driver which illustrates many concepts -discussed above and plus it handles both PCI and SBUS boards. - - drivers/scsi/esp.c - Check it out for scatter-gather DVMA. - - drivers/sbus/char/bpp.c - A non-DVMA device. - - drivers/net/sunlance.c - Lance driver abuses consistent mappings for data transfer. -It is a nifty trick which we do not particularly recommend... -Just check it out and know that it's legal. |