diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/DMA-API.txt | 49 | ||||
| -rw-r--r-- | Documentation/DMA-mapping.txt | 22 | ||||
| -rw-r--r-- | Documentation/i2c/busses/i2c-parport | 16 |
3 files changed, 63 insertions, 24 deletions
diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index 1af0f2d..2ffb0d6 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -33,7 +33,9 @@ pci_alloc_consistent(struct pci_dev *dev, size_t size, Consistent memory is memory for which a write by either the device or the processor can immediately be read by the processor or device -without having to worry about caching effects. +without having to worry about caching effects. (You may however need +to make sure to flush the processor's write buffers before telling +devices to read that memory.) This routine allocates a region of <size> bytes of consistent memory. it also returns a <dma_handle> which may be cast to an unsigned @@ -304,12 +306,12 @@ dma address with dma_mapping_error(). A non zero return value means the mapping could not be created and the driver should take appropriate action (eg reduce current DMA mapping usage or delay and try again later). -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) + 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) Maps a scatter gather list from the block layer. @@ -327,12 +329,33 @@ critical that the driver do something, in the case of a block driver aborting the request or even oopsing is better than doing nothing and corrupting the filesystem. -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) +With scatterlists, you use the resulting mapping like this: + + int i, count = dma_map_sg(dev, sglist, nents, direction); + struct scatterlist *sg; + + for (i = 0, sg = sglist; i < count; i++, sg++) { + hw_address[i] = sg_dma_address(sg); + hw_len[i] = sg_dma_len(sg); + } + +where nents is the number of entries in the sglist. + +The implementation is free to merge several consecutive sglist entries +into one (e.g. with an IOMMU, or if several pages just happen to be +physically contiguous) and returns the actual number of sg entries it +mapped them to. On failure 0, is returned. + +Then you should loop count times (note: this can be less than nents times) +and use sg_dma_address() and sg_dma_len() macros where you previously +accessed sg->address and sg->length as shown above. + + 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 diff --git a/Documentation/DMA-mapping.txt b/Documentation/DMA-mapping.txt index 10bf4de..7c717699 100644 --- a/Documentation/DMA-mapping.txt +++ b/Documentation/DMA-mapping.txt @@ -58,11 +58,15 @@ translating each of those pages back to a kernel address using 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(). @@ -284,6 +288,11 @@ There are two types of DMA mappings: 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. @@ -303,6 +312,9 @@ There are two types of DMA mappings: 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. diff --git a/Documentation/i2c/busses/i2c-parport b/Documentation/i2c/busses/i2c-parport index d9f23c0..77b995d 100644 --- a/Documentation/i2c/busses/i2c-parport +++ b/Documentation/i2c/busses/i2c-parport @@ -12,18 +12,22 @@ meant as a replacement for the older, individual drivers: teletext adapters) It currently supports the following devices: - * Philips adapter - * home brew teletext adapter - * Velleman K8000 adapter - * ELV adapter - * Analog Devices evaluation boards (ADM1025, ADM1030, ADM1031, ADM1032) - * Barco LPT->DVI (K5800236) adapter + * (type=0) Philips adapter + * (type=1) home brew teletext adapter + * (type=2) Velleman K8000 adapter + * (type=3) ELV adapter + * (type=4) Analog Devices ADM1032 evaluation board + * (type=5) Analog Devices evaluation boards: ADM1025, ADM1030, ADM1031 + * (type=6) Barco LPT->DVI (K5800236) adapter These devices use different pinout configurations, so you have to tell the driver what you have, using the type module parameter. There is no way to autodetect the devices. Support for different pinout configurations can be easily added when needed. +Earlier kernels defaulted to type=0 (Philips). But now, if the type +parameter is missing, the driver will simply fail to initialize. + Building your own adapter ------------------------- |
