Alignment problems: arm_memblock_steal() + dma_declare_coherent_memory()
From: javier Martin <hidden>
Date: 2012-09-14 08:49:28
Hello, we use arm_memblock_steal() + dma_declare_coherent_memory() in order to reserve son contiguous video memory in our platform: http://git.linuxtv.org/media_tree.git/blob/refs/heads/staging/for_v3.7:/arch/arm/mach-imx/mach-imx27_visstrim_m10.c We've noticed that some restrictive alignment constraints are being applied. For example, for coda driver, the following allocations are made: coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 557056 bytes, out of 8388608 (vaddr = 0xc6000000) PAGE_SHIFT = 0xc coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 65536 bytes, out of 8388608 (vaddr = 0xc6100000) PAGE_SHIFT = 0xc coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 10240 bytes, out of 8388608 (vaddr = 0xc6110000) PAGE_SHIFT = 0xc coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 622080 bytes, out of 8388608 (vaddr = 0xc6200000) PAGE_SHIFT = 0xc coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 622080 bytes, out of 8388608 (vaddr = 0xc6300000) PAGE_SHIFT = 0xc coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 622080 bytes, out of 8388608 (vaddr = 0xc6400000) PAGE_SHIFT = 0xc coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 589824 bytes, out of 8388608 (vaddr = 0xc6500000) PAGE_SHIFT = 0xc coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 589824 bytes, out of 8388608 (vaddr = 0xc6600000) PAGE_SHIFT = 0xc coda coda-imx27.0: dma_alloc_from_coherent: try to allocate 622080 bytes, out of 8388608 (vaddr = 0xc6700000) PAGE_SHIFT = 0xc If we take a look at the size of each allocation and the different vaddr values we find that the alignment is 0x100000 = 1MB for values like 622080 byte size. Why is that? A lot of memory is being wasted this way and our HW does not have such 1MB alignment requirements. Regards. -- Javier Martin Vista Silicon S.L. CDTUC - FASE C - Oficina S-345 Avda de los Castros s/n 39005- Santander. Cantabria. Spain +34 942 25 32 60 www.vista-silicon.com