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I'm porting / debugging a device driver (that is used by another kernel module) and facing a dead end because dma_sync_single_for_device() fails with an kernel oops.
I have no clue what that function is supposed to do and googling does not really help, so I probably need to learn more about this stuff in total.
The question is, where to start?
Oh yeah, in case it is relevant, the code is supposed to run on a PowerPC (and the linux is OpenWRT)
EDIT: On-line resources preferrable (books take a few days to be delivered :)
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Linux provides a framework that allows most DMA hardware to be supported in a general way. The framework, known as the DMA Engine, provides the infrastructure for DMA drivers to plug into and then be accessed from kernel space with another client driver using a standard API.
Direct memory access, or DMA, is the advanced topic that completes our overview of memory issues. DMA is the hardware mechanism that allows peripheral components to transfer their I/O data directly to and from main memory without the need for the system processor to be involved in the transfer.
Linux-based operating systems use a virtual memory system. Any address referenced by a user-space application must be translated into a physical address. This is achieved through a combination of page tables and address translation hardware in the underlying computer system.
Sysctl vm. min_free_kbytes shows the amount of memory which the kernel keeps free for kernel memory allocations.
On-line:
Anatomy of the Linux slab allocator
Understanding the Linux Virtual Memory Manager
Linux Device Drivers, Third Edition
The Linux Kernel Module Programming Guide
Writing device drivers in Linux: A brief tutorial
Books:
Linux Kernel Development (2nd Edition)
Essential Linux Device Drivers ( Only the first 4 - 5 chapters )
Useful Resources:
the Linux Cross Reference ( Searchable Kernel Source for all Kernels )
API changes in the 2.6 kernel series
dma_sync_single_for_device calls dma_sync_single_range_for_cpu a little further up in the file and this is the source documentation ( I assume that even though this is for arm the interface and behavior are the same ):
/**
380 * dma_sync_single_range_for_cpu
381 * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
382 * @handle: DMA address of buffer
383 * @offset: offset of region to start sync
384 * @size: size of region to sync
385 * @dir: DMA transfer direction (same as passed to dma_map_single)
386 *
387 * Make physical memory consistent for a single streaming mode DMA
388 * translation after a transfer.
389 *
390 * If you perform a dma_map_single() but wish to interrogate the
391 * buffer using the cpu, yet do not wish to teardown the PCI dma
392 * mapping, you must call this function before doing so. At the
393 * next point you give the PCI dma address back to the card, you
394 * must first the perform a dma_sync_for_device, and then the
395 * device again owns the buffer.
396 */
Understanding The Linux Kernel?
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