Re: [PATCH] instmem/gk20a: do not use non-portable dma_to_phys()

[Dave Airlie]

On 11 November 2015 at 08:41, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 10 Nov 2015 14:10:47 +0900 Alexandre Courbot <acourbot@xxxxxxxxxx> wrote:
>
>> dma_to_phys() is not guaranteed to be available on all platforms and
>> should not be used outside of arch/. Replace it with what it is expected
>> to do in our case: simply cast the DMA handle to a physical address.
>
> mainline i386 allmodconfig is now busted.

I'll push my hack to make things build into drm-fixes while we discuss
the subtlety.

Dave.
>
>> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/gk20a.c
>> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/gk20a.c
>> @@ -134,13 +134,17 @@ static void __iomem *
>>  gk20a_instobj_cpu_map_dma(struct nvkm_memory *memory)
>>  {
>>       struct gk20a_instobj_dma *node = gk20a_instobj_dma(memory);
>> -     struct device *dev = node->base.imem->base.subdev.device->dev;
>>       int npages = nvkm_memory_size(memory) >> 12;
>>       struct page *pages[npages];
>>       int i;
>>
>> -     /* phys_to_page does not exist on all platforms... */
>> -     pages[0] = pfn_to_page(dma_to_phys(dev, node->handle) >> PAGE_SHIFT);
>> +     /*
>> +      * Ideally we would have a function to translate a handle to a physical
>> +      * address, but there is no portable way of doing this. However since we
>> +      * always use the DMA API without an IOMMU, we can assume that handles
>> +      * are actual physical addresses.
>> +      */
>> +     pages[0] = pfn_to_page(((phys_addr_t)node->handle) >> PAGE_SHIFT);
>
> This looks ugly.
>
> What's actually going on here?  Why is this driver doing something which
> no other driver appears to need to do?
>
> Is it the driver which is broken, or are the core kernel APIs inadequate?
>
> If the latter, what can we do to fix them up?
>
> IOW, how do we fix this properly?
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/