sparc: Remove Documentation/sparc/sbus_drivers.txt

None of the text in this document is relevant any more.

Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/sparc/sbus_drivers.txt

@@ -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.