linux-kernel - Re: [PATCH v3 6/6] Documentation: dmaengine: document DMA_CTRL

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Message-ID: <87twvekij8.fsf@belgarion.home>
Date:	Thu, 14 May 2015 22:31:39 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Jonathan Corbet <corbet@....net>,
	Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	dmaengine@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 6/6] Documentation: dmaengine: document DMA_CTRL_ACK

Maxime Ripard <maxime.ripard@...e-electrons.com> writes:

> Hi Robert,
>
>>    * DMA_CTRL_ACK
>> -    - Undocumented feature
>> -    - No one really has an idea of what it's about, besides being
>> -      related to reusing the DMA transaction descriptors or having
>> -      additional transactions added to it in the async-tx API
>> -    - Useless in the case of the slave API
>> +    - if set, the TX transfer can be reused after being completed.
>
> Your sentences should start with an upper-case letter.
Ack.

>> +    - there is a guarantee the TX won't be freed until it is acked
>> +      by async_tx_ack()
>
> We never talked about what a "TX transfer" is in the
> documentation. That should be documented.
I'll remove the "TX", the transfer is widely used in this documentation.

>
>> +    - as a consequence, if a device driver wants to skip the dma_map_sg() and
>> +      dma_unmap_sg() because the DMA'd data wasn't used, it can resubmit the
>> +      transfer right after its completion.
>
> From a provider PoV, the data should always be mapped and / or
> allocated in coherent way, so I'm not sure how does that's relevant in
> the provider doc.
It's relevant because it says the mapping/unmapping is not necessary _between_ 2
submission of a transfer. This implies it is mapped, as it is a requirement for
the very first submission.

> Also, we should still mention that it's !slave API only.
Certainly not, it's fully slave API, that's the purpose of this patch.

-- 
Robert
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