linux-kernel - Re: [PATCH v3 09/13] dmaengine: tegra-apb: Remove runtime PM usage

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Date:   Tue, 7 Jan 2020 15:13:52 +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 v3 09/13] dmaengine: tegra-apb: Remove runtime PM usage


On 06/01/2020 01:17, Dmitry Osipenko wrote:
> There is no benefit from runtime PM usage for the APB DMA driver because
> it enables clock at the time of channel's allocation and thus clock stays
> enabled all the time in practice, secondly there is benefit from manually
> disabled clock because hardware auto-gates it during idle by itself.

This assumes that the channel is allocated during a driver
initialisation. That may not always be the case. I believe audio is one
case where channels are requested at the start of audio playback.

Jon

-- 
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