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From:   Peng Fan <peng.fan@nxp.com>
To:     Mark Brown <broonie@kernel.org>
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        "S.j. Wang" <shengjiu.wang@nxp.com>
Subject: RE: [PATCH] regmap: mmio: prepare/unprepare clk only when read/write
Thread-Topic: [PATCH] regmap: mmio: prepare/unprepare clk only when read/write
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Date:   Fri, 24 Apr 2020 01:27:29 +0000
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> Subject: Re: [PATCH] regmap: mmio: prepare/unprepare clk only when
> read/write
>=20
> On Thu, Apr 23, 2020 at 10:51:36AM +0000, Peng Fan wrote:
>=20
> > > 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.
>=20
> > 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.
>=20
> Not really in regmap itself - I think your best bet here is to move the c=
lock
> 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 probab=
ly
> going to be able to do a better job pushing this into rutime PM in the dr=
iver or
> just having direct clock calls.

If we not pass clk to regmap, accessing regmap registers will hang system w=
ith
Debugfs enabled.

If we pass clk to regmap, it will make the runtime pm power high, because
regmap mmio will call clk_prepare at the beginning.

That's why use clk_prepare_enable and clk_disable_unprepare.

Thinking about another direction, how about add clk_prepare and clk_unprepa=
re
into debugfs ops open/close?

Thanks,
Peng.