view Documentation/sparc/sbus_drivers.txt @ 452:c7ed6fe5dca0

kexec: dont initialise regions in reserve_memory()

There is no need to initialise efi_memmap_res and boot_param_res in
reserve_memory() for the initial xen domain as it is done in
machine_kexec_setup_resources() using values from the kexec hypercall.

Signed-off-by: Simon Horman <horms@verge.net.au>
author Keir Fraser <keir.fraser@citrix.com>
date Thu Feb 28 10:55:18 2008 +0000 (2008-02-28)
parents 831230e53067
line source
2 Writing SBUS Drivers
4 David S. Miller (davem@redhat.com)
6 The SBUS driver interfaces of the Linux kernel have been
7 revamped completely for 2.4.x for several reasons. Foremost were
8 performance and complexity concerns. This document details these
9 new interfaces and how they are used to write an SBUS device driver.
11 SBUS drivers need to include <asm/sbus.h> to get access
12 to functions and structures described here.
14 Probing and Detection
16 Each SBUS device inside the machine is described by a
17 structure called "struct sbus_dev". Likewise, each SBUS bus
18 found in the system is described by a "struct sbus_bus". For
19 each SBUS bus, the devices underneath are hung in a tree-like
20 fashion off of the bus structure.
22 The SBUS device structure contains enough information
23 for you to implement your device probing algorithm and obtain
24 the bits necessary to run your device. The most commonly
25 used members of this structure, and their typical usage,
26 will be detailed below.
28 Here is a piece of skeleton code for perofming a device
29 probe in an SBUS driverunder Linux:
31 static int __devinit mydevice_probe_one(struct sbus_dev *sdev)
32 {
33 struct mysdevice *mp = kzalloc(sizeof(*mp), GFP_KERNEL);
35 if (!mp)
36 return -ENODEV;
38 ...
39 dev_set_drvdata(&sdev->ofdev.dev, mp);
40 return 0;
41 ...
42 }
44 static int __devinit mydevice_probe(struct of_device *dev,
45 const struct of_device_id *match)
46 {
47 struct sbus_dev *sdev = to_sbus_device(&dev->dev);
49 return mydevice_probe_one(sdev);
50 }
52 static int __devexit mydevice_remove(struct of_device *dev)
53 {
54 struct sbus_dev *sdev = to_sbus_device(&dev->dev);
55 struct mydevice *mp = dev_get_drvdata(&dev->dev);
57 return mydevice_remove_one(sdev, mp);
58 }
60 static struct of_device_id mydevice_match[] = {
61 {
62 .name = "mydevice",
63 },
64 {},
65 };
67 MODULE_DEVICE_TABLE(of, mydevice_match);
69 static struct of_platform_driver mydevice_driver = {
70 .name = "mydevice",
71 .match_table = mydevice_match,
72 .probe = mydevice_probe,
73 .remove = __devexit_p(mydevice_remove),
74 };
76 static int __init mydevice_init(void)
77 {
78 return of_register_driver(&mydevice_driver, &sbus_bus_type);
79 }
81 static void __exit mydevice_exit(void)
82 {
83 of_unregister_driver(&mydevice_driver);
84 }
86 module_init(mydevice_init);
87 module_exit(mydevice_exit);
89 The mydevice_match table is a series of entries which
90 describes what SBUS devices your driver is meant for. In the
91 simplest case you specify a string for the 'name' field. Every
92 SBUS device with a 'name' property matching your string will
93 be passed one-by-one to your .probe method.
95 You should store away your device private state structure
96 pointer in the drvdata area so that you can retrieve it later on
97 in your .remove method.
99 Any memory allocated, registers mapped, IRQs registered,
100 etc. must be undone by your .remove method so that all resources
101 of your device are relased by the time it returns.
103 You should _NOT_ use the for_each_sbus(), for_each_sbusdev(),
104 and for_all_sbusdev() interfaces. They are deprecated, will be
105 removed, and no new driver should reference them ever.
107 Mapping and Accessing I/O Registers
109 Each SBUS device structure contains an array of descriptors
110 which describe each register set. We abuse struct resource for that.
111 They each correspond to the "reg" properties provided by the OBP firmware.
113 Before you can access your device's registers you must map
114 them. And later if you wish to shutdown your driver (for module
115 unload or similar) you must unmap them. You must treat them as
116 a resource, which you allocate (map) before using and free up
117 (unmap) when you are done with it.
119 The mapping information is stored in an opaque value
120 typed as an "unsigned long". This is the type of the return value
121 of the mapping interface, and the arguments to the unmapping
122 interface. Let's say you want to map the first set of registers.
123 Perhaps part of your driver software state structure looks like:
125 struct mydevice {
126 unsigned long control_regs;
127 ...
128 struct sbus_dev *sdev;
129 ...
130 };
132 At initialization time you then use the sbus_ioremap
133 interface to map in your registers, like so:
135 static void init_one_mydevice(struct sbus_dev *sdev)
136 {
137 struct mydevice *mp;
138 ...
140 mp->control_regs = sbus_ioremap(&sdev->resource[0], 0,
141 CONTROL_REGS_SIZE, "mydevice regs");
142 if (!mp->control_regs) {
143 /* Failure, cleanup and return. */
144 }
145 }
147 Second argument to sbus_ioremap is an offset for
148 cranky devices with broken OBP PROM. The sbus_ioremap uses only
149 a start address and flags from the resource structure.
150 Therefore it is possible to use the same resource to map
151 several sets of registers or even to fabricate a resource
152 structure if driver gets physical address from some private place.
153 This practice is discouraged though. Use whatever OBP PROM
154 provided to you.
156 And here is how you might unmap these registers later at
157 driver shutdown or module unload time, using the sbus_iounmap
158 interface:
160 static void mydevice_unmap_regs(struct mydevice *mp)
161 {
162 sbus_iounmap(mp->control_regs, CONTROL_REGS_SIZE);
163 }
165 Finally, to actually access your registers there are 6
166 interface routines at your disposal. Accesses are byte (8 bit),
167 word (16 bit), or longword (32 bit) sized. Here they are:
169 u8 sbus_readb(unsigned long reg) /* read byte */
170 u16 sbus_readw(unsigned long reg) /* read word */
171 u32 sbus_readl(unsigned long reg) /* read longword */
172 void sbus_writeb(u8 value, unsigned long reg) /* write byte */
173 void sbus_writew(u16 value, unsigned long reg) /* write word */
174 void sbus_writel(u32 value, unsigned long reg) /* write longword */
176 So, let's say your device has a control register of some sort
177 at offset zero. The following might implement resetting your device:
179 #define CONTROL 0x00UL
181 #define CONTROL_RESET 0x00000001 /* Reset hardware */
183 static void mydevice_reset(struct mydevice *mp)
184 {
185 sbus_writel(CONTROL_RESET, mp->regs + CONTROL);
186 }
188 Or perhaps there is a data port register at an offset of
189 16 bytes which allows you to read bytes from a fifo in the device:
191 #define DATA 0x10UL
193 static u8 mydevice_get_byte(struct mydevice *mp)
194 {
195 return sbus_readb(mp->regs + DATA);
196 }
198 It's pretty straightforward, and clueful readers may have
199 noticed that these interfaces mimick the PCI interfaces of the
200 Linux kernel. This was not by accident.
204 DO NOT try to treat these opaque register mapping
205 values as a memory mapped pointer to some structure
206 which you can dereference.
208 It may be memory mapped, it may not be. In fact it
209 could be a physical address, or it could be the time
210 of day xor'd with 0xdeadbeef. :-)
212 Whatever it is, it's an implementation detail. The
213 interface was done this way to shield the driver
214 author from such complexities.
216 Doing DVMA
218 SBUS devices can perform DMA transactions in a way similar
219 to PCI but dissimilar to ISA, e.g. DMA masters supply address.
220 In contrast to PCI, however, that address (a bus address) is
221 translated by IOMMU before a memory access is performed and therefore
222 it is virtual. Sun calls this procedure DVMA.
224 Linux supports two styles of using SBUS DVMA: "consistent memory"
225 and "streaming DVMA". CPU view of consistent memory chunk is, well,
226 consistent with a view of a device. Think of it as an uncached memory.
227 Typically this way of doing DVMA is not very fast and drivers use it
228 mostly for control blocks or queues. On some CPUs we cannot flush or
229 invalidate individual pages or cache lines and doing explicit flushing
230 over ever little byte in every control block would be wasteful.
232 Streaming DVMA is a preferred way to transfer large amounts of data.
233 This process works in the following way:
234 1. a CPU stops accessing a certain part of memory,
235 flushes its caches covering that memory;
236 2. a device does DVMA accesses, then posts an interrupt;
237 3. CPU invalidates its caches and starts to access the memory.
239 A single streaming DVMA operation can touch several discontiguous
240 regions of a virtual bus address space. This is called a scatter-gather
241 DVMA.
243 [TBD: Why do not we neither Solaris attempt to map disjoint pages
244 into a single virtual chunk with the help of IOMMU, so that non SG
245 DVMA masters would do SG? It'd be very helpful for RAID.]
247 In order to perform a consistent DVMA a driver does something
248 like the following:
250 char *mem; /* Address in the CPU space */
251 u32 busa; /* Address in the SBus space */
253 mem = (char *) sbus_alloc_consistent(sdev, MYMEMSIZE, &busa);
255 Then mem is used when CPU accesses this memory and u32
256 is fed to the device so that it can do DVMA. This is typically
257 done with an sbus_writel() into some device register.
259 Do not forget to free the DVMA resources once you are done:
261 sbus_free_consistent(sdev, MYMEMSIZE, mem, busa);
263 Streaming DVMA is more interesting. First you allocate some
264 memory suitable for it or pin down some user pages. Then it all works
265 like this:
267 char *mem = argumen1;
268 unsigned int size = argument2;
269 u32 busa; /* Address in the SBus space */
271 *mem = 1; /* CPU can access */
272 busa = sbus_map_single(sdev, mem, size);
273 if (busa == 0) .......
275 /* Tell the device to use busa here */
276 /* CPU cannot access the memory without sbus_dma_sync_single() */
278 sbus_unmap_single(sdev, busa, size);
279 if (*mem == 0) .... /* CPU can access again */
281 It is possible to retain mappings and ask the device to
282 access data again and again without calling sbus_unmap_single.
283 However, CPU caches must be invalidated with sbus_dma_sync_single
284 before such access.
286 [TBD but what about writeback caches here... do we have any?]
288 There is an equivalent set of functions doing the same thing
289 only with several memory segments at once for devices capable of
290 scatter-gather transfers. Use the Source, Luke.
292 Examples
294 drivers/net/sunhme.c
295 This is a complicated driver which illustrates many concepts
296 discussed above and plus it handles both PCI and SBUS boards.
298 drivers/scsi/esp.c
299 Check it out for scatter-gather DVMA.
301 drivers/sbus/char/bpp.c
302 A non-DVMA device.
304 drivers/net/sunlance.c
305 Lance driver abuses consistent mappings for data transfer.
306 It is a nifty trick which we do not particularly recommend...
307 Just check it out and know that it's legal.