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 <[email protected]> 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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