linux-kernel - RE: [PATCH] regmap: mmio: prepare/unprepare clk only when read/write

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Date:   Thu, 23 Apr 2020 10:51:36 +0000
From:   Peng Fan <peng.fan@....com>
To:     Mark Brown <broonie@...nel.org>
CC:     "rafael@...nel.org" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "S.j. Wang" <shengjiu.wang@....com>
Subject: RE: [PATCH] regmap: mmio: prepare/unprepare clk only when read/write

> Subject: Re: [PATCH] regmap: mmio: prepare/unprepare clk only when
> read/write
> 
> On Thu, Apr 23, 2020 at 01:46:31PM +0800, peng.fan@....com wrote:
> > From: Peng Fan <peng.fan@....com>
> >
> > use clk_prepare at the very beginning will invoke pm runtime resume,
> > if the clk is binded with a power domain. This will cause runtime
> > power high. Let's use clk_prepare_enable and clk_disable_unprepare
> > when read/write to avoid the runtime power issue.
> 
> This will mean that we're doing clk_prepare() during I/O which isn't good
> since for MMIO regmaps we support I/O operations in atomic contexts.

Ah, yes. Do you have any suggestions? If we use clk_prepare at the very
beginning, the power that binded to the clk device will be always on,
and cause power consumption high.

Thanks,
Peng.