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

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Date:   Thu, 23 Apr 2020 12:22:44 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Peng Fan <peng.fan@....com>
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

On Thu, Apr 23, 2020 at 10:51:36AM +0000, Peng Fan wrote:

> > 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.

Not really in regmap itself - I think your best bet here is to move the
clock handling out of regmap and up into the driver.  regmap won't do
any I/O unless your driver calls it so this will work fine, this support
is only there in regmap as a convenience but if it's getting in the way
then you're probably going to be able to do a better job pushing this
into rutime PM in the driver or just having direct clock calls.

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