[RFC v2 PATCH 1/3] ARM: NOMMU: introduce dma operations for noMMU

[Benjamin Gaignard]

2017-01-04 11:33 GMT+01:00 Vladimir Murzin <vladimir.murzin at arm.com>:
> Hello Benjamin,
>
> On 02/01/17 15:26, Benjamin Gaignard wrote:
>> Hello Vladimir,
>>
>> I have tested your patch on my setup (stm32f4: no MMU, no MPU) where
>> I'm writing display driver.
>> This driver use dma_alloc_wc() and dma_mmap_wc() for frame buffer
>> allocation and mmapping.
>>
>> In dma-mapping-nommu.c you haven't implement dma_map_ops.mmap so
>> obviously my driver
>> doesn't work with your code.
>> In current implementation it is buggy too but I submit a patch to fix
>> that problem:
>> http://www.armlinux.org.uk/developer/patches/viewpatch.php?id=8633/1
>>
>> Could it be possible for you to include mmap support in dma-mapping-nommu.c ?
>>
>
> IIRC, stm32f4 is Cortex-M4, so no cache support and it means that it uses
> dma_noop_ops. I offloaded mmap to common implementation, but completely forgot
> it has the same restriction as arm counterpart. Regardless, thanks for
> noticing that!
>
> It seems that I need to check that mapping is done from DMA coherent area (I'm
> moving to dma-coherent and here we have dma_mmap_from_coherent for that) and
> something like bellow for dma_noop_ops:
>
> diff --git a/lib/dma-noop.c b/lib/dma-noop.c
> index 3d766e7..d838b88 100644
> --- a/lib/dma-noop.c
> +++ b/lib/dma-noop.c
> @@ -64,6 +64,25 @@ static int dma_noop_supported(struct device *dev, u64 mask)
>         return 1;
>  }
>
> +static int dma_noop_mmap(struct device *dev, struct vm_area_struct *vma,
> +                        void *cpu_addr, dma_addr_t dma_addr, size_t size)
> +{
> +       unsigned long user_count = vma_pages(vma);
> +       unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +       unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr));
> +       unsigned long off = vma->vm_pgoff;
> +       int ret = -ENXIO;
> +
> +       if (off < count && user_count <= (count - off)) {
> +               ret = remap_pfn_range(vma, vma->vm_start,
> +                                     pfn + off,
> +                                     user_count << PAGE_SHIFT,
> +                                     vma->vm_page_prot);
> +       }
> +
> +       return ret;
> +}
> +
>  struct dma_map_ops dma_noop_ops = {
>         .alloc                  = dma_noop_alloc,
>         .free                   = dma_noop_free,
> @@ -71,6 +90,7 @@ struct dma_map_ops dma_noop_ops = {
>         .map_sg                 = dma_noop_map_sg,
>         .mapping_error          = dma_noop_mapping_error,
>         .dma_supported          = dma_noop_supported,
> +       .mmap                   = dma_noop_mmap,
>  };
>
>  EXPORT_SYMBOL(dma_noop_ops);
>
> I'd be glad to hear if it works for you.

With your patch mmap() does return an address unfortunately
framebuffer isn't displayed
anymore, I have a black screen instead of the usual pattern.

Without your patches my allocations dma_alloc_wc requests go to
dma-mapping so I guess
the problem is coming from dma noop implementation.
I have try to use dma-mapping-nommu ops but the status is the same.

>
> Cheers
> Vladimir
>
>> Regards,
>> Benjamin



-- 
Benjamin Gaignard

Graphic Study Group

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