linux-kernel - Re: [PATCH v6 11/16] dmaengine: tegra-apb: Keep clock enabled only during of DMA transfer

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Date:   Fri, 31 Jan 2020 09:02:28 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Vinod Koul <vkoul@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>
CC:     <dmaengine@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 11/16] dmaengine: tegra-apb: Keep clock enabled only
 during of DMA transfer


On 30/01/2020 20:04, Dmitry Osipenko wrote:

...

>>> The tegra_dma_stop() should put RPM anyways, which is missed in yours
>>> sample. Please see handle_continuous_head_request().
>>
>> Yes and that is deliberate. The cyclic transfers the transfers *should*
>> not stop until terminate_all is called. The tegra_dma_stop in
>> handle_continuous_head_request() is an error condition and so I am not
>> sure it is actually necessary to call pm_runtime_put() here.
> 
> But then tegra_dma_stop() shouldn't unset the "busy" mark.

True.

>>> I'm also finding the explicit get/put a bit easier to follow in the
>>> code, don't you think so?
>>
>> I can see that, but I was thinking that in the case of cyclic transfers,
>> it should only really be necessary to call the get/put at the beginning
>> and end. So in my mind there should only be two exit points which are
>> the ISR handler for SG and terminate_all for SG and cyclic.
> 
> Alright, I'll update this patch.

Hmmm ... I am wondering if we should not mess with that and leave how
you have it.

-- 
nvpublic