On February 1, 2019 4:17:50 AM UTC, Vinod Koul <vk...@kernel.org> wrote:
>On 28-01-19, 09:47, Federico Vaga wrote:
>> Hi,
>>
>> I have a new question concerning documentation.
>>
>>
>https://www.kernel.org/doc/html/latest/driver-api/dmaengine/client.html
>>
>> >From this document it is not really clear, at least to me, if
>clients can
>> consider valid the `struct dma_async_tx_descriptor` after submission
>to the
>> DMA engine.
>
>Nope they can't and should not touch the descriptor after submission.
>The client get cookie and that is supposed to be used
Good, thanks
>>
>> Clients get a TX descriptor from a DMA engine using things like
>> `dmaengine_prep_*`. These calls - may - allocate new descriptors and
>return
>> them to the caller; this may include other structures which are not
>visible to
>> clients. So, if my understanding is correct, this means that it's the
>DMA
>> engine that, on TX completion, releases any TX descriptor allocated
>by
>> `dmaengine_prep_*`. This implies that the pointer that the client is
>using
>> must be considered invalid right after `dmaengine_submit()`.
>> If what I understood by reading the documentation and the code is
>correct,
>> then I think that this should be mentioned in the Documentation.
>> If I'm wrong, please tell me where :)
>
>And what exactly are you trying to do here..?
What if I answer: "the right thing"? Joking. I just expressed my understanding
of something which is not documented properly (my opinion). I wanted to be sure
that the logic, the reasons behind are the ones that I understood. I will
propose a patch to the documentation, unless you want to do it.
--
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