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From:   Brian Norris <briannorris@chromium.org>
Date:   Fri, 4 Feb 2022 12:05:07 -0800
Message-ID: <CA+ASDXO-61=D0DM+d4dNCbEYV3omroFbbFao3YrUPOYy+7AJUg@mail.gmail.com>
Subject: Re: regmap: mmio: lack of runtime_pm support for debugfs
To:     Mark Brown <broonie@kernel.org>
Cc:     Peng Fan <peng.fan@nxp.com>,
        "rafael@kernel.org" <rafael@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>,
        "S.j. Wang" <shengjiu.wang@nxp.com>
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After a bit more thinking:

On Fri, Feb 4, 2022 at 11:21 AM Brian Norris <briannorris@chromium.org> wrote:
> Anyway, I'll probably just go with precious_reg() as suggested above.

Unfortunately, precious_reg() wouldn't be quite safe either -- we
could do a single check for pm_runtime_active(), but we have no way of
knowing (guaranteeing) that it will remain active throughout the
remainder of the debugfs operation. For all we know, some other actor
could be *just* finishing with (and PM-suspending) our domain
immediately after the check. And we can't grab a reference, because we
don't have a callback for balancing that back out.

If I really want to solve this, I might have to go with adding a
debugfs-specific runtime_pm flag, and (to avoid too many side effects)
use that with pm_runtime_get_if_active() in regmap-debugfs.c.

Brian