Re: [PATCH v7 08/36] drm: exynos: fix common struct sg_table related issues

[Andrzej Hajda <a.hajda@samsung.com>]

On 07.07.2020 11:40, Andrzej Hajda wrote:
> On 19.06.2020 12:36, Marek Szyprowski wrote:
>> The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
>> returns the number of the created entries in the DMA address space.
>> However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
>> dma_unmap_sg must be called with the original number of the entries
>> passed to the dma_map_sg().
>>
>> struct sg_table is a common structure used for describing a non-contiguous
>> memory buffer, used commonly in the DRM and graphics subsystems. It
>> consists of a scatterlist with memory pages and DMA addresses (sgl entry),
>> as well as the number of scatterlist entries: CPU pages (orig_nents entry)
>> and DMA mapped pages (nents entry).
>>
>> It turned out that it was a common mistake to misuse nents and orig_nents
>> entries, calling DMA-mapping functions with a wrong number of entries or
>> ignoring the number of mapped entries returned by the dma_map_sg()
>> function.
>>
>> To avoid such issues, lets use a common dma-mapping wrappers operating
>> directly on the struct sg_table objects and use scatterlist page
>> iterators where possible. This, almost always, hides references to the
>> nents and orig_nents entries, making the code robust, easier to follow
>> and copy/paste safe.
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>

Just fixing my signature :)

Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>

Regards
Andrzej

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