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Date:   Fri, 1 Feb 2019 09:59:22 +0000
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Subject: Re: DMA Engine Documentation: TX Descriptor and Submission
To:     Vinod Koul <vkoul@kernel.org>
CC:     <dmaengine@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-doc@vger.kernel.org>
From:   Federico Vaga <federico.vaga@cern.ch>
Message-ID: <77C59695-001C-46B3-9C41-C4C7A763D001@cern.ch>
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On February 1, 2019 4:17:50 AM UTC, Vinod Koul <vkoul@kernel=2Eorg> wrote:
>On 28-01-19, 09:47, Federico Vaga wrote:
>> Hi,
>>=20
>> I have a new question concerning documentation=2E
>>=20
>>
>https://www=2Ekernel=2Eorg/doc/html/latest/driver-api/dmaengine/client=2E=
html
>>=20
>> >From this document it is not really clear, at least to me, if
>clients can=20
>> consider valid the `struct dma_async_tx_descriptor` after submission
>to the=20
>> DMA engine=2E
>
>Nope they can't and should not touch the descriptor after submission=2E
>The client get cookie and that is supposed to be used

Good, thanks


>>=20
>> Clients get a TX descriptor from a DMA engine using things like=20
>> `dmaengine_prep_*`=2E These calls - may - allocate new descriptors and
>return=20
>> them to the caller; this may include other structures which are not
>visible to=20
>> clients=2E So, if my understanding is correct, this means that it's the
>DMA=20
>> engine that, on TX completion, releases any TX descriptor allocated
>by=20
>> `dmaengine_prep_*`=2E This implies that the pointer that the client is
>using=20
>> must be considered invalid right after `dmaengine_submit()`=2E
>> If what I understood by reading the documentation and the code is
>correct,=20
>> then I think that this should be mentioned in the Documentation=2E
>> If I'm wrong, please tell me where :)
>
>And what exactly are you trying to do here=2E=2E?

What if I answer: "the right thing"? Joking=2E I just expressed my underst=
anding of something which is not documented properly (my opinion)=2E I want=
ed to be sure that the logic, the reasons behind are the ones that I unders=
tood=2E I will propose a patch to the documentation, unless you want to do =
it=2E
--=20
Inviato dal mio dispositivo Android con K-9 Mail=2E Perdonate la brevit=C3=
=A0=2E