James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
This document describes the DMA API. For a more gentle introduction
-phrased in terms of the pci_ equivalents (and actual examples) see
-DMA-mapping.txt
+of the API (and actual examples) see
+Documentation/DMA-API-HOWTO.txt.
-This API is split into two pieces. Part I describes the API and the
-corresponding pci_ API. Part II describes the extensions to the API
-for supporting non-consistent memory machines. Unless you know that
-your driver absolutely has to support non-consistent platforms (this
-is usually only legacy platforms) you should only use the API
-described in part I.
+This API is split into two pieces. Part I describes the API. Part II
+describes the extensions to the API for supporting non-consistent
+memory machines. Unless you know that your driver absolutely has to
+support non-consistent platforms (this is usually only legacy
+platforms) you should only use the API described in part I.
-Part I - pci_ and dma_ Equivalent API
+Part I - dma_ API
-------------------------------------
-To get the pci_ API, you must #include <linux/pci.h>
To get the dma_ API, you must #include <linux/dma-mapping.h>
void *
dma_alloc_coherent(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t flag)
-void *
-pci_alloc_consistent(struct pci_dev *dev, size_t size,
- dma_addr_t *dma_handle)
Consistent memory is memory for which a write by either the device or
the processor can immediately be read by the processor or device
The flag parameter (dma_alloc_coherent only) allows the caller to
specify the GFP_ flags (see kmalloc) for the allocation (the
implementation may choose to ignore flags that affect the location of
-the returned memory, like GFP_DMA). For pci_alloc_consistent, you
-must assume GFP_ATOMIC behaviour.
+the returned memory, like GFP_DMA).
void
dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
dma_addr_t dma_handle)
-void
-pci_free_consistent(struct pci_dev *dev, size_t size, void *cpu_addr,
- dma_addr_t dma_handle)
Free the region of consistent memory you previously allocated. dev,
size and dma_handle must all be the same as those passed into the
dma_pool_create(const char *name, struct device *dev,
size_t size, size_t align, size_t alloc);
- struct pci_pool *
- pci_pool_create(const char *name, struct pci_device *dev,
- size_t size, size_t align, size_t alloc);
-
The pool create() routines initialize a pool of dma-coherent buffers
for use with a given device. It must be called in a context which
can sleep.
void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags,
dma_addr_t *dma_handle);
- void *pci_pool_alloc(struct pci_pool *pool, gfp_t gfp_flags,
- dma_addr_t *dma_handle);
-
This allocates memory from the pool; the returned memory will meet the size
and alignment requirements specified at creation time. Pass GFP_ATOMIC to
prevent blocking, or if it's permitted (not in_interrupt, not holding SMP locks),
void dma_pool_free(struct dma_pool *pool, void *vaddr,
dma_addr_t addr);
- void pci_pool_free(struct pci_pool *pool, void *vaddr,
- dma_addr_t addr);
-
This puts memory back into the pool. The pool is what was passed to
the pool allocation routine; the cpu (vaddr) and dma addresses are what
were returned when that routine allocated the memory being freed.
void dma_pool_destroy(struct dma_pool *pool);
- void pci_pool_destroy(struct pci_pool *pool);
-
The pool destroy() routines free the resources of the pool. They must be
called in a context which can sleep. Make sure you've freed all allocated
memory back to the pool before you destroy it.
int
dma_supported(struct device *dev, u64 mask)
-int
-pci_dma_supported(struct pci_dev *hwdev, u64 mask)
Checks to see if the device can support DMA to the memory described by
mask.
int
dma_set_mask(struct device *dev, u64 mask)
+
+Checks to see if the mask is possible and updates the device
+parameters if it is.
+
+Returns: 0 if successful and a negative error if not.
+
int
-pci_set_dma_mask(struct pci_device *dev, u64 mask)
+dma_set_coherent_mask(struct device *dev, u64 mask)
Checks to see if the mask is possible and updates the device
parameters if it is.
dma_addr_t
dma_map_single(struct device *dev, void *cpu_addr, size_t size,
enum dma_data_direction direction)
-dma_addr_t
-pci_map_single(struct pci_dev *hwdev, void *cpu_addr, size_t size,
- int direction)
Maps a piece of processor virtual memory so it can be accessed by the
device and returns the physical handle of the memory.
However the dma_ API uses a strongly typed enumerator for its
direction:
-DMA_NONE = PCI_DMA_NONE no direction (used for
- debugging)
-DMA_TO_DEVICE = PCI_DMA_TODEVICE data is going from the
- memory to the device
-DMA_FROM_DEVICE = PCI_DMA_FROMDEVICE data is coming from
- the device to the
- memory
-DMA_BIDIRECTIONAL = PCI_DMA_BIDIRECTIONAL direction isn't known
+DMA_NONE no direction (used for debugging)
+DMA_TO_DEVICE data is going from the memory to the device
+DMA_FROM_DEVICE data is coming from the device to the memory
+DMA_BIDIRECTIONAL direction isn't known
Notes: Not all memory regions in a machine can be mapped by this
API. Further, regions that appear to be physically contiguous in
void
dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
enum dma_data_direction direction)
-void
-pci_unmap_single(struct pci_dev *hwdev, dma_addr_t dma_addr,
- size_t size, int direction)
Unmaps the region previously mapped. All the parameters passed in
must be identical to those passed in (and returned) by the mapping
dma_map_page(struct device *dev, struct page *page,
unsigned long offset, size_t size,
enum dma_data_direction direction)
-dma_addr_t
-pci_map_page(struct pci_dev *hwdev, struct page *page,
- unsigned long offset, size_t size, int direction)
void
dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
enum dma_data_direction direction)
-void
-pci_unmap_page(struct pci_dev *hwdev, dma_addr_t dma_address,
- size_t size, int direction)
API for mapping and unmapping for pages. All the notes and warnings
for the other mapping APIs apply here. Also, although the <offset>
int
dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
-int
-pci_dma_mapping_error(struct pci_dev *hwdev, dma_addr_t dma_addr)
-
In some circumstances dma_map_single and dma_map_page will fail to create
a mapping. A driver can check for these errors by testing the returned
dma address with dma_mapping_error(). A non-zero return value means the mapping
int
dma_map_sg(struct device *dev, struct scatterlist *sg,
int nents, enum dma_data_direction direction)
- int
- pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,
- int nents, int direction)
Returns: the number of physical segments mapped (this may be shorter
than <nents> passed in if some elements of the scatter/gather list are
void
dma_unmap_sg(struct device *dev, struct scatterlist *sg,
int nhwentries, enum dma_data_direction direction)
- void
- pci_unmap_sg(struct pci_dev *hwdev, struct scatterlist *sg,
- int nents, int direction)
Unmap the previously mapped scatter/gather list. All the parameters
must be the same as those and passed in to the scatter/gather mapping
physical entries returned.
void
-dma_sync_single(struct device *dev, dma_addr_t dma_handle, size_t size,
- enum dma_data_direction direction)
+dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
+ enum dma_data_direction direction)
void
-pci_dma_sync_single(struct pci_dev *hwdev, dma_addr_t dma_handle,
- size_t size, int direction)
+dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, size_t size,
+ enum dma_data_direction direction)
void
-dma_sync_sg(struct device *dev, struct scatterlist *sg, int nelems,
- enum dma_data_direction direction)
+dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems,
+ enum dma_data_direction direction)
void
-pci_dma_sync_sg(struct pci_dev *hwdev, struct scatterlist *sg,
- int nelems, int direction)
+dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nelems,
+ enum dma_data_direction direction)
-Synchronise a single contiguous or scatter/gather mapping. All the
-parameters must be the same as those passed into the single mapping
-API.
+Synchronise a single contiguous or scatter/gather mapping for the cpu
+and device. With the sync_sg API, all the parameters must be the same
+as those passed into the single mapping API. With the sync_single API,
+you can use dma_handle and size parameters that aren't identical to
+those passed into the single mapping API to do a partial sync.
Notes: You must do this:
Part II - Advanced dma_ usage
-----------------------------
-Warning: These pieces of the DMA API have no PCI equivalent. They
-should also not be used in the majority of cases, since they cater for
-unlikely corner cases that don't belong in usual drivers.
+Warning: These pieces of the DMA API should not be used in the
+majority of cases, since they cater for unlikely corner cases that
+don't belong in usual drivers.
If you don't understand how cache line coherency works between a
processor and an I/O device, you should not be using this part of the
of two for easy alignment.
void
-dma_sync_single_range(struct device *dev, dma_addr_t dma_handle,
- unsigned long offset, size_t size,
- enum dma_data_direction direction)
-
-Does a partial sync, starting at offset and continuing for size. You
-must be careful to observe the cache alignment and width when doing
-anything like this. You must also be extra careful about accessing
-memory you intend to sync partially.
-
-void
dma_cache_sync(struct device *dev, void *vaddr, size_t size,
enum dma_data_direction direction)
The return value will be either a pointer to the processor virtual
address of the memory, or an error (via PTR_ERR()) if any part of the
region is occupied.
+
+Part III - Debug drivers use of the DMA-API
+-------------------------------------------
+
+The DMA-API as described above as some constraints. DMA addresses must be
+released with the corresponding function with the same size for example. With
+the advent of hardware IOMMUs it becomes more and more important that drivers
+do not violate those constraints. In the worst case such a violation can
+result in data corruption up to destroyed filesystems.
+
+To debug drivers and find bugs in the usage of the DMA-API checking code can
+be compiled into the kernel which will tell the developer about those
+violations. If your architecture supports it you can select the "Enable
+debugging of DMA-API usage" option in your kernel configuration. Enabling this
+option has a performance impact. Do not enable it in production kernels.
+
+If you boot the resulting kernel will contain code which does some bookkeeping
+about what DMA memory was allocated for which device. If this code detects an
+error it prints a warning message with some details into your kernel log. An
+example warning message may look like this:
+
+------------[ cut here ]------------
+WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448
+ check_unmap+0x203/0x490()
+Hardware name:
+forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong
+ function [device address=0x00000000640444be] [size=66 bytes] [mapped as
+single] [unmapped as page]
+Modules linked in: nfsd exportfs bridge stp llc r8169
+Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1
+Call Trace:
+ <IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130
+ [<ffffffff80647b70>] _spin_unlock+0x10/0x30
+ [<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0
+ [<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40
+ [<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0
+ [<ffffffff80252f96>] queue_work+0x56/0x60
+ [<ffffffff80237e10>] enqueue_task_fair+0x20/0x50
+ [<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0
+ [<ffffffff803b78c3>] cpumask_next_and+0x23/0x40
+ [<ffffffff80235177>] find_busiest_group+0x207/0x8a0
+ [<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50
+ [<ffffffff803c7ea3>] check_unmap+0x203/0x490
+ [<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50
+ [<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0
+ [<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0
+ [<ffffffff8026df84>] handle_IRQ_event+0x34/0x70
+ [<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150
+ [<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0
+ [<ffffffff8020c093>] ret_from_intr+0x0/0xa
+ <EOI> <4>---[ end trace f6435a98e2a38c0e ]---
+
+The driver developer can find the driver and the device including a stacktrace
+of the DMA-API call which caused this warning.
+
+Per default only the first error will result in a warning message. All other
+errors will only silently counted. This limitation exist to prevent the code
+from flooding your kernel log. To support debugging a device driver this can
+be disabled via debugfs. See the debugfs interface documentation below for
+details.
+
+The debugfs directory for the DMA-API debugging code is called dma-api/. In
+this directory the following files can currently be found:
+
+ dma-api/all_errors This file contains a numeric value. If this
+ value is not equal to zero the debugging code
+ will print a warning for every error it finds
+ into the kernel log. Be careful with this
+ option, as it can easily flood your logs.
+
+ dma-api/disabled This read-only file contains the character 'Y'
+ if the debugging code is disabled. This can
+ happen when it runs out of memory or if it was
+ disabled at boot time
+
+ dma-api/error_count This file is read-only and shows the total
+ numbers of errors found.
+
+ dma-api/num_errors The number in this file shows how many
+ warnings will be printed to the kernel log
+ before it stops. This number is initialized to
+ one at system boot and be set by writing into
+ this file
+
+ dma-api/min_free_entries
+ This read-only file can be read to get the
+ minimum number of free dma_debug_entries the
+ allocator has ever seen. If this value goes
+ down to zero the code will disable itself
+ because it is not longer reliable.
+
+ dma-api/num_free_entries
+ The current number of free dma_debug_entries
+ in the allocator.
+
+ dma-api/driver-filter
+ You can write a name of a driver into this file
+ to limit the debug output to requests from that
+ particular driver. Write an empty string to
+ that file to disable the filter and see
+ all errors again.
+
+If you have this code compiled into your kernel it will be enabled by default.
+If you want to boot without the bookkeeping anyway you can provide
+'dma_debug=off' as a boot parameter. This will disable DMA-API debugging.
+Notice that you can not enable it again at runtime. You have to reboot to do
+so.
+
+If you want to see debug messages only for a special device driver you can
+specify the dma_debug_driver=<drivername> parameter. This will enable the
+driver filter at boot time. The debug code will only print errors for that
+driver afterwards. This filter can be disabled or changed later using debugfs.
+
+When the code disables itself at runtime this is most likely because it ran
+out of dma_debug_entries. These entries are preallocated at boot. The number
+of preallocated entries is defined per architecture. If it is too low for you
+boot with 'dma_debug_entries=<your_desired_number>' to overwrite the
+architectural default.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff