Messages in this thread Patch in this message | | | Date | Mon, 7 Dec 2015 13:28:24 +0000 | From | Brian Starkey <> | Subject | Re: [PATCH] drivers: dma-coherent: use ioremap_wc() for DMA_MEMORY_MAP |
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On Fri, Dec 04, 2015 at 05:15:54PM +0000, Catalin Marinas wrote: >On Fri, Dec 04, 2015 at 08:59:10AM -0800, Dan Williams wrote: >> On Fri, Dec 4, 2015 at 2:50 AM, Catalin Marinas <catalin.marinas@arm.com> wrote: >> > On Fri, Nov 20, 2015 at 02:20:26PM +0000, Brian Starkey wrote: >> >> When the DMA_MEMORY_MAP flag is used, memory which can be accessed >> >> directly should be returned, so use ioremap_wc() instead of ioremap(). >> >> Also, ensure that the correct memset operation is used in >> >> dma_alloc_from_coherent() with respect to the region's flags. >> >> >> >> This fixes the below alignment fault on arm64, caused by invalid use >> >> of memset() on Device memory. >> > >> > This is indeed affecting both arm32 and arm64 systems. >> > >> >> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c >> >> index 55b8398..45358d0 100644 >> >> --- a/drivers/base/dma-coherent.c >> >> +++ b/drivers/base/dma-coherent.c >> >> @@ -31,7 +31,10 @@ static int dma_init_coherent_memory(phys_addr_t phys_addr, dma_addr_t device_add >> >> if (!size) >> >> goto out; >> >> >> >> - mem_base = ioremap(phys_addr, size); >> >> + if (flags & DMA_MEMORY_MAP) >> >> + mem_base = ioremap_wc(phys_addr, size); >> >> + else >> >> + mem_base = ioremap(phys_addr, size); >> > >> > I wonder whether a memremap() approach for the DMA_MEMORY_MAP case would >> > be better. This API was added recently by commit 92281dee825f ("arch: >> > introduce memremap()"). It only supports write-back and write-through >> > but we could add a MEMREMAP_WC flag for this case. >> >> I originally included both MEMREMAP_WC and MEMREAMP_UC as potential >> flags to this api, but ultimately decided against it. The memremap() >> api is meant for memory that is known to have no i/o side effects. As >> far as I can see WC and UC usages are a muddy mix of "sometimes >> there's I/O side effects, but it depends by arch and driver". In >> other words we can't drop the "__iomem" annotation from WC and UC >> mappings by default.
The DMA_MEMORY_MAP flag is pretty much a statement of "no side- effects", so as Catalin says it would fit OK here. That said, if it's not possible to deprecate ioremap_wc() in the same way as ioremap_cache() then I wonder if there's even much benefit in adding it to memremap().
> >In this context, the dma_declare_coherent_memory(DMA_MEMORY_MAP) >implementation is aimed at normal RAM with no side effects as later >returned by dma_alloc_coherent(). To me it looks like memremap is better >suited here for the DMA_MEMORY_MAP case. As per the >Documentation/DMA-API.txt: > > DMA_MEMORY_MAP - request that the memory returned from > dma_alloc_coherent() be directly writable. > >which means no __iomem. Of course, we still need ioremap for >DMA_MEMORY_IO which is supposed to be written with memcpy_toio() etc. > >Which memory type should be used is left to the driver and it should >pass the corresponding DMA_MEMORY_* flag. >
This can still be achieved without adding _WC to memremap(). I can look at adding _WC to memremap() if that's deemed the preferred approach, but if that isn't clear-cut, then it would be nice to get this bug fixed now and worry about adding it to memremap() later.
-Brian
>-- Catalin >
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