transfer.
The following API will work of course even on platforms where no such
-hardware exists, see e.g. include/asm-i386/pci.h for how it is implemented on
+hardware exists, see e.g. arch/x86/include/asm/pci.h for how it is implemented on
top of the virt_to_bus interface.
First of all, you should make sure
something like __va(). [ EDIT: Update this when we integrate
Gerd Knorr's generic code which does this. ]
-This rule also means that you may not use kernel image addresses
-(ie. items in the kernel's data/text/bss segment, or your driver's)
-nor may you use kernel stack addresses for DMA. Both of these items
-might be mapped somewhere entirely different than the rest of physical
-memory.
+This rule also means that you may use neither kernel image addresses
+(items in data/text/bss segments), nor module image addresses, nor
+stack addresses for DMA. These could all be mapped somewhere entirely
+different than the rest of physical memory. Even if those classes of
+memory could physically work with DMA, you'd need to ensure the I/O
+buffers were cacheline-aligned. Without that, you'd see cacheline
+sharing problems (data corruption) on CPUs with DMA-incoherent caches.
+(The CPU could write to one word, DMA would write to a different one
+in the same cache line, and one of them could be overwritten.)
Also, this means that you cannot take the return of a kmap()
call and DMA to/from that. This is similar to vmalloc().
int pci_set_dma_mask(struct pci_dev *pdev, u64 device_mask);
-The query for consistent allocations is performed via a a call to
+The query for consistent allocations is performed via a call to
pci_set_consistent_dma_mask():
int pci_set_consistent_dma_mask(struct pci_dev *pdev, u64 device_mask);
device supports. It returns zero if your card can perform DMA
properly on the machine given the address mask you provided.
-If it returns non-zero, your device can not perform DMA properly on
+If it returns non-zero, your device cannot perform DMA properly on
this platform, and attempting to do so will result in undefined
behavior. You must either use a different mask, or not use DMA.
device driver only uses consistent allocations, one would have to
check the return value from pci_set_consistent_dma_mask().
-If your 64-bit device is going to be an enormous consumer of DMA
-mappings, this can be problematic since the DMA mappings are a
-finite resource on many platforms. Please see the "DAC Addressing
-for Address Space Hungry Devices" section near the end of this
-document for how to handle this case.
-
Finally, if your device can only drive the low 24-bits of
address during PCI bus mastering you might do something like:
- if (pci_set_dma_mask(pdev, 0x00ffffff)) {
+ if (pci_set_dma_mask(pdev, DMA_24BIT_MASK)) {
printk(KERN_WARNING
"mydev: 24-bit DMA addressing not available.\n");
goto ignore_this_device;
}
-[Better use DMA_24BIT_MASK instead of 0x00ffffff.
-See linux/include/dma-mapping.h for reference.]
When pci_set_dma_mask() is successful, and returns zero, the PCI layer
saves away this mask you have provided. The PCI layer will use this
functions) and the various different functions have _different_
DMA addressing limitations, you may wish to probe each mask and
only provide the functionality which the machine can handle. It
-is important that the last call to pci_set_dma_mask() be for the
+is important that the last call to pci_set_dma_mask() be for the
most specific mask.
Here is pseudo-code showing how this might be done:
in order to get correct behavior on all platforms.
+ Also, on some platforms your driver may need to flush CPU write
+ buffers in much the same way as it needs to flush write buffers
+ found in PCI bridges (such as by reading a register's value
+ after writing it).
+
- Streaming DMA mappings which are usually mapped for one DMA transfer,
unmapped right after it (unless you use pci_dma_sync_* below) and for which
hardware can optimize for sequential accesses.
Neither type of DMA mapping has alignment restrictions that come
from PCI, although some devices may have such restrictions.
+Also, systems with caches that aren't DMA-coherent will work better
+when the underlying buffers don't share cache lines with other data.
+
Using Consistent DMA mappings.
dma_addr_t dma_handle;
- cpu_addr = pci_alloc_consistent(dev, size, &dma_handle);
+ cpu_addr = pci_alloc_consistent(pdev, size, &dma_handle);
-where dev is a struct pci_dev *. You should pass NULL for PCI like buses
-where devices don't have struct pci_dev (like ISA, EISA). This may be
-called in interrupt context.
+where pdev is a struct pci_dev *. This may be called in interrupt context.
+You should use dma_alloc_coherent (see DMA-API.txt) for buses
+where devices don't have struct pci_dev (like ISA, EISA).
This argument is needed because the DMA translations may be bus
specific (and often is private to the bus which the device is attached
driver needs regions sized smaller than a page, you may prefer using
the pci_pool interface, described below.
-The consistent DMA mapping interfaces, for non-NULL dev, will by
+The consistent DMA mapping interfaces, for non-NULL pdev, will by
default return a DMA address which is SAC (Single Address Cycle)
addressable. Even if the device indicates (via PCI dma mask) that it
may address the upper 32-bits and thus perform DAC cycles, consistent
To unmap and free such a DMA region, you call:
- pci_free_consistent(dev, size, cpu_addr, dma_handle);
+ pci_free_consistent(pdev, size, cpu_addr, dma_handle);
-where dev, size are the same as in the above call and cpu_addr and
+where pdev, size are the same as in the above call and cpu_addr and
dma_handle are the values pci_alloc_consistent returned to you.
This function may not be called in interrupt context.
struct pci_pool *pool;
- pool = pci_pool_create(name, dev, size, align, alloc);
+ pool = pci_pool_create(name, pdev, size, align, alloc);
-The "name" is for diagnostics (like a kmem_cache name); dev and size
+The "name" is for diagnostics (like a kmem_cache name); pdev and size
are as above. The device's hardware alignment requirement for this
type of data is "align" (which is expressed in bytes, and must be a
power of two). If your device has no boundary crossing restrictions,
void *addr = buffer->ptr;
size_t size = buffer->len;
- dma_handle = pci_map_single(dev, addr, size, direction);
+ dma_handle = pci_map_single(pdev, addr, size, direction);
and to unmap it:
- pci_unmap_single(dev, dma_handle, size, direction);
+ pci_unmap_single(pdev, dma_handle, size, direction);
You should call pci_unmap_single when the DMA activity is finished, e.g.
from the interrupt which told you that the DMA transfer is done.
unsigned long offset = buffer->offset;
size_t size = buffer->len;
- dma_handle = pci_map_page(dev, page, offset, size, direction);
+ dma_handle = pci_map_page(pdev, page, offset, size, direction);
...
- pci_unmap_page(dev, dma_handle, size, direction);
+ pci_unmap_page(pdev, dma_handle, size, direction);
Here, "offset" means byte offset within the given page.
With scatterlists, you map a region gathered from several regions by:
- int i, count = pci_map_sg(dev, sglist, nents, direction);
+ int i, count = pci_map_sg(pdev, sglist, nents, direction);
struct scatterlist *sg;
- for (i = 0, sg = sglist; i < count; i++, sg++) {
+ for_each_sg(sglist, sg, count, i) {
hw_address[i] = sg_dma_address(sg);
hw_len[i] = sg_dma_len(sg);
}
To unmap a scatterlist, just call:
- pci_unmap_sg(dev, sglist, nents, direction);
+ pci_unmap_sg(pdev, sglist, nents, direction);
Again, make sure DMA activity has already finished.
So, firstly, just map it with pci_map_{single,sg}, and after each DMA
transfer call either:
- pci_dma_sync_single_for_cpu(dev, dma_handle, size, direction);
+ pci_dma_sync_single_for_cpu(pdev, dma_handle, size, direction);
or:
- pci_dma_sync_sg_for_cpu(dev, sglist, nents, direction);
+ pci_dma_sync_sg_for_cpu(pdev, sglist, nents, direction);
as appropriate.
finish accessing the data with the cpu, and then before actually
giving the buffer to the hardware call either:
- pci_dma_sync_single_for_device(dev, dma_handle, size, direction);
+ pci_dma_sync_single_for_device(pdev, dma_handle, size, direction);
or:
they are entirely deprecated. Some ports already do not provide these
as it is impossible to correctly support them.
- 64-bit DMA and DAC cycle support
-
-Do you understand all of the text above? Great, then you already
-know how to use 64-bit DMA addressing under Linux. Simply make
-the appropriate pci_set_dma_mask() calls based upon your cards
-capabilities, then use the mapping APIs above.
-
-It is that simple.
-
-Well, not for some odd devices. See the next section for information
-about that.
-
- DAC Addressing for Address Space Hungry Devices
-
-There exists a class of devices which do not mesh well with the PCI
-DMA mapping API. By definition these "mappings" are a finite
-resource. The number of total available mappings per bus is platform
-specific, but there will always be a reasonable amount.
-
-What is "reasonable"? Reasonable means that networking and block I/O
-devices need not worry about using too many mappings.
-
-As an example of a problematic device, consider compute cluster cards.
-They can potentially need to access gigabytes of memory at once via
-DMA. Dynamic mappings are unsuitable for this kind of access pattern.
-
-To this end we've provided a small API by which a device driver
-may use DAC cycles to directly address all of physical memory.
-Not all platforms support this, but most do. It is easy to determine
-whether the platform will work properly at probe time.
-
-First, understand that there may be a SEVERE performance penalty for
-using these interfaces on some platforms. Therefore, you MUST only
-use these interfaces if it is absolutely required. %99 of devices can
-use the normal APIs without any problems.
-
-Note that for streaming type mappings you must either use these
-interfaces, or the dynamic mapping interfaces above. You may not mix
-usage of both for the same device. Such an act is illegal and is
-guaranteed to put a banana in your tailpipe.
-
-However, consistent mappings may in fact be used in conjunction with
-these interfaces. Remember that, as defined, consistent mappings are
-always going to be SAC addressable.
-
-The first thing your driver needs to do is query the PCI platform
-layer with your devices DAC addressing capabilities:
-
- int pci_dac_set_dma_mask(struct pci_dev *pdev, u64 mask);
-
-This routine behaves identically to pci_set_dma_mask. You may not
-use the following interfaces if this routine fails.
-
-Next, DMA addresses using this API are kept track of using the
-dma64_addr_t type. It is guaranteed to be big enough to hold any
-DAC address the platform layer will give to you from the following
-routines. If you have consistent mappings as well, you still
-use plain dma_addr_t to keep track of those.
-
-All mappings obtained here will be direct. The mappings are not
-translated, and this is the purpose of this dialect of the DMA API.
-
-All routines work with page/offset pairs. This is the _ONLY_ way to
-portably refer to any piece of memory. If you have a cpu pointer
-(which may be validly DMA'd too) you may easily obtain the page
-and offset using something like this:
-
- struct page *page = virt_to_page(ptr);
- unsigned long offset = offset_in_page(ptr);
-
-Here are the interfaces:
-
- dma64_addr_t pci_dac_page_to_dma(struct pci_dev *pdev,
- struct page *page,
- unsigned long offset,
- int direction);
-
-The DAC address for the tuple PAGE/OFFSET are returned. The direction
-argument is the same as for pci_{map,unmap}_single(). The same rules
-for cpu/device access apply here as for the streaming mapping
-interfaces. To reiterate:
-
- The cpu may touch the buffer before pci_dac_page_to_dma.
- The device may touch the buffer after pci_dac_page_to_dma
- is made, but the cpu may NOT.
-
-When the DMA transfer is complete, invoke:
-
- void pci_dac_dma_sync_single_for_cpu(struct pci_dev *pdev,
- dma64_addr_t dma_addr,
- size_t len, int direction);
-
-This must be done before the CPU looks at the buffer again.
-This interface behaves identically to pci_dma_sync_{single,sg}_for_cpu().
-
-And likewise, if you wish to let the device get back at the buffer after
-the cpu has read/written it, invoke:
-
- void pci_dac_dma_sync_single_for_device(struct pci_dev *pdev,
- dma64_addr_t dma_addr,
- size_t len, int direction);
-
-before letting the device access the DMA area again.
-
-If you need to get back to the PAGE/OFFSET tuple from a dma64_addr_t
-the following interfaces are provided:
-
- struct page *pci_dac_dma_to_page(struct pci_dev *pdev,
- dma64_addr_t dma_addr);
- unsigned long pci_dac_dma_to_offset(struct pci_dev *pdev,
- dma64_addr_t dma_addr);
-
-This is possible with the DAC interfaces purely because they are
-not translated in any way.
-
Optimizing Unmap State Space Consumption
On many platforms, pci_unmap_{single,page}() is simply a nop.
dma_addr_t dma_handle;
- dma_handle = pci_map_single(dev, addr, size, direction);
- if (pci_dma_mapping_error(dma_handle)) {
+ dma_handle = pci_map_single(pdev, addr, size, direction);
+ if (pci_dma_mapping_error(pdev, dma_handle)) {
/*
* reduce current DMA mapping usage,
* delay and try again later or
Jay Estabrook <Jay.Estabrook@compaq.com>
Thomas Sailer <sailer@ife.ee.ethz.ch>
Andrea Arcangeli <andrea@suse.de>
- Jens Axboe <axboe@suse.de>
+ Jens Axboe <jens.axboe@oracle.com>
David Mosberger-Tang <davidm@hpl.hp.com>
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff