Messages in this thread | | | Date | Mon, 7 Dec 2015 08:19:27 -0800 | Subject | Re: [PATCH] drivers: dma-coherent: use ioremap_wc() for DMA_MEMORY_MAP | From | Dan Williams <> |
| |
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).
| |