linux-kernel - Re: [PATCH v2 2/8] clk: Introduce CLK_ASSUME_ENABLED_WHEN

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Message-ID: <CAG3jFysjzTMJM=DbLGNXBfWYjQKxxRvGQMZp6GOL7uBvRUwRYw@mail.gmail.com>
Date:   Tue, 3 May 2022 18:23:45 +0200
From:   Robert Foss <robert.foss@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     agross@...nel.org, mturquette@...libre.com, sboyd@...nel.org,
        robh+dt@...nel.org, krzk+dt@...nel.org, jonathan@...ek.ca,
        tdas@...eaurora.org, anischal@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v2 2/8] clk: Introduce CLK_ASSUME_ENABLED_WHEN_UNUSED

On Tue, 3 May 2022 at 17:02, Bjorn Andersson <bjorn.andersson@...aro.org> wrote:
>
> On Tue 03 May 08:04 CDT 2022, Robert Foss wrote:
>
> > From: Bjorn Andersson <bjorn.andersson@...aro.org>
> >
> > Some clock implementations doesn't provide means of implementing
> > is_enabled(), but still requires to be explicitly disabled when found
> > unused as part of clk_disable_unused().
> >
> > One such set of clocks are Qualcomm's display RCGs. These can be enabled
> > and disabled automatically by the hardware, so it's not possible to
> > reliably query their configuration. Further more, these clocks need to
> > be disabled when unused, to allow them to be "parked" onto a safe
> > parent. Failure to disable the RCG results in the hardware locking up as
> > clk_disable_unused() traverses up the tree and turns off its source
> > clocks.
> >
> > Add a new flag, CLK_ASSUME_ENABLED_BOOT, which clock drivers can use to
> > signal that these clocks should be disabled even if they don't implement
> > the is_enabled() ops.
> >
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> >
>
> I discussed this with Stephen a while ago and we agreed that in a
> sufficiently complex system with kernel modules booting without
> clk_ignore_unused simply isn't supported.
>
> We will have to design something better. So please drop this patch from
> the series.

Ack