linux-kernel - Re: [PATCH] clk: qcom: gdsc: Keep RETAIN

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Message-ID: <CAD=FV=WYFTu-J5L6usJNWtjH-FWe+o8JYWNxVYBdg5-coWaQag@mail.gmail.com>
Date:   Mon, 19 Oct 2020 07:58:06 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Taniya Das <tdas@...eaurora.org>,
        Rajendra Nayak <rnayak@...eaurora.org>
Subject: Re: [PATCH] clk: qcom: gdsc: Keep RETAIN_FF bit set if gdsc is
 already on

Hi,

On Fri, Oct 16, 2020 at 7:01 PM Stephen Boyd <sboyd@...nel.org> wrote:
>
> If the GDSC is enabled out of boot but doesn't have the retain ff bit
> set we will get confusing results where the registers that are powered
> by the GDSC lose their contents on the first power off of the GDSC but
> thereafter they retain their contents. This is because gdsc_init() fails
> to make sure the RETAIN_FF bit is set when it probes the GDSC the first
> time and thus powering off the GDSC causes the register contents to be
> reset. We do set the RETAIN_FF bit the next time we power on the GDSC,
> see gdsc_enable(), so that subsequent GDSC power off's don't lose
> register contents state.
>
> Forcibly set the bit at device probe time so that the kernel's assumed
> view of the GDSC is consistent with the state of the hardware. This
> fixes a problem where the audio PLL doesn't work on sc7180 when the
> bootloader leaves the lpass_core_hm GDSC enabled at boot (e.g. to make a
> noise) but critically doesn't set the RETAIN_FF bit.
>
> Cc: Douglas Anderson <dianders@...omium.org>
> Cc: Taniya Das <tdas@...eaurora.org>
> Cc: Rajendra Nayak <rnayak@...eaurora.org>
> Fixes: 173722995cdb ("clk: qcom: gdsc: Add support to enable retention of GSDCR")
> Signed-off-by: Stephen Boyd <sboyd@...nel.org>
> ---
>  drivers/clk/qcom/gdsc.c | 8 ++++++++
>  1 file changed, 8 insertions(+)

Reviewed-by: Douglas Anderson <dianders@...omium.org>
Tested-by: Douglas Anderson <dianders@...omium.org>