Messages in this thread | | | Date | Mon, 7 Dec 2015 16:47:15 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH] drivers: dma-coherent: use ioremap_wc() for DMA_MEMORY_MAP |
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On Mon, Dec 07, 2015 at 08:19:27AM -0800, Dan Williams wrote: > On Mon, Dec 7, 2015 at 5:28 AM, Brian Starkey <brian.starkey@arm.com> wrote: > > 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(). > > I don't see a problem adding a _WC option to memremap. > > The only difference is that it can't replace ioremap_wc. I.e. unlike > _WB, and _WT case where ioremap_cache and ioremap_wt are now > deprecated we'd have ioremap_wc continuing to live alongside > memremap(..., MEMREMAP_WC).
I think that's fine. The difference is that memory returned by ioremap_wc() should (in theory) only be accessed with I/O accessors while the range returned by memremap(MEMREMAP_WC) will be directly accessible.
-- Catalin
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