|From:||James Bottomley <James.Bottomley@steeleye.com>|
|To:||Ian Molton <email@example.com>|
|Subject:||[RFC] on-chip coherent memory API for DMA|
|Date:||29 Jun 2004 09:21:05 -0500|
|Cc:||Linux Kernel <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, Russell King <email@example.com>|
The purpose of this API is to find a way of declaring on-chip memory as a pool for dma_alloc_coherent() that can be useful to all architectures. The proposed API is: nt dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr, dma_addr_t device_addr, size_t size, int flags) This API basically declares a region of memory to be handed out by dma_alloc_coherent when it's asked for coherent memory for this device. bus_addr is the physical address to which the memory is currently assigned in the bus responding region device_addr is the physical address the device needs to be programmed with actually to address this memory. size is the size of the area (must be multiples of PAGE_SIZE). The flags is where all the magic is. They can be or'd together and are DMA_MEMORY_MAP - request that the memory returned from dma_alloc_coherent() be directly writeable. DMA_MEMORY_IO - request that the memory returned from dma_alloc_coherent() be addressable using read/write/memcpy_toio etc. One or both of these flags must be present DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by dma_alloc_coherent of any child devices of this one (for memory residing on a bridge). DMA_MEMORY_EXCLUSIVE - only allocate memory from the declared regions. Do not allow dma_alloc_coherent() to fall back to system memory when it's out of memory in the declared region. The return value would be either DMA_MEMORY_MAP or DMA_MEMORY_IO and must correspond to a passed in flag (i.e. no returning DMA_MEMORY_IO if only DMA_MEMORY_MAP were passed in) or zero for failure. I think also, it's reasonable only to have a single declared region per device. Implementation details Obviously, the big change is that dma_alloc_coherent() may now be handing out memory that can't be directly written to (in the case of a DMA_MEMORY_IO return). I envisage implementing an internal per device resource allocator in drivers/base into which each platform allocator can plug do do the heavy allocation lifting (they'd still get to do the platform magic to make the returned region visible as memory if necessary). The API would be platform optional, with platforms not wishing to implement it simply hard coding a return 0. There would also be a corresponding void dma_release_declared_memory(struct device *dev) whose job would be to clean up unconditionally (and not check if the memory were still in use). I already have this coded up on x86 and implemented for a SCSI card I have with four channels and a shared 2MB memory area on chip. I'll post the implementations when I get it cleaned up. James - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to firstname.lastname@example.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Copyright © 2004, Eklektix, Inc.
Comments and public postings are copyrighted by their creators.
Linux is a registered trademark of Linus Torvalds