Re: [PATCH 6/8] drivers: add Contiguous Memory Allocator
On Wed, 6 Jul 2011, Russell King - ARM Linux wrote: they typically don't fall into the highmem zone. As the dmabounce code allocates from the DMA coherent allocator to provide it with guaranteed DMA-able memory, that would be rather inconvenient. True. The dmabounce code would consequently have to allocate the memory through an internal function that avoids the contiguous allocation area and goes straight to ZONE_DMA memory as it does today. CMA's whole purpose for existing is to provide _dma-able_ contiguous memory for things like cameras and such like found on crippled non- scatter-gather hardware. If that memory is not DMA-able what's the point? ZONE_DMA is a zone for memory of legacy (crippled) devices that cannot DMA into all of memory (and so is ZONE_DMA32). Memory from ZONE_NORMAL can be used for DMA as well and a fully capable device would be expected to handle any memory in the system for DMA transfers. guaranteed dmaable memory? DMA abilities are device specific. Well maybe you can call ZONE_DMA memory to be guaranteed if you guarantee that any device must at mininum be able to perform DMA into ZONE_DMA memory. But there may not be much of that memory around so you would want to limit the use of that scarce resource. -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 6/8] drivers: add Contiguous Memory Allocator
On Wed, 6 Jul 2011, Michal Nazarewicz wrote: On Wed, 06 Jul 2011 18:05:00 +0200, Christoph Lameter c...@linux.com wrote: ZONE_DMA is a zone for memory of legacy (crippled) devices that cannot DMA into all of memory (and so is ZONE_DMA32). Memory from ZONE_NORMAL can be used for DMA as well and a fully capable device would be expected to handle any memory in the system for DMA transfers. guaranteed dmaable memory? DMA abilities are device specific. Well maybe you can call ZONE_DMA memory to be guaranteed if you guarantee that any device must at mininum be able to perform DMA into ZONE_DMA memory. But there may not be much of that memory around so you would want to limit the use of that scarce resource. As pointed in Marek's other mail, this reasoning is not helping in any way. In case of video codec on various Samsung devices (and from some other threads this is not limited to Samsung), the codec needs separate buffers in separate memory banks. What I described is the basic memory architecture of Linux. I am not that familiar with ARM and the issue discussed here. Only got involved because ZONE_DMA was mentioned. The nature of ZONE_DMA is often misunderstood. The allocation of the memory banks for the Samsung devices has to fit somehow into one of these zones. Its probably best to put the memory banks into ZONE_NORMAL and not have any dependency on ZONE_DMA at all. -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 6/8] drivers: add Contiguous Memory Allocator
On Wed, 6 Jul 2011, Russell King - ARM Linux wrote: So, ARM is no different from x86, with the exception that the 16MB DMA zone due to ISA ends up being different sizes on ARM depending on our restrictions. Sounds good. Thank you. -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
