linux-kernel - Re: [PATCH 1/2] clk: qcom: gcc-sm8550: Don't use parking clk

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Message-ID: <CAE-0n51fjJ8QO2eAy5ZbQOwo9Urzrv1NnXw6KzB=mwHoVoJKzw@mail.gmail.com>
Date: Tue, 27 Aug 2024 13:04:01 -0500
From: Stephen Boyd <swboyd@...omium.org>
To: Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Stephen Boyd <sboyd@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	patches@...ts.linux.dev, linux-clk@...r.kernel.org, 
	Konrad Dybcio <konradybcio@...nel.org>, Taniya Das <quic_tdas@...cinc.com>, 
	Amit Pundir <amit.pundir@...aro.org>
Subject: Re: [PATCH 1/2] clk: qcom: gcc-sm8550: Don't use parking clk_ops for QUPs

Quoting Stephen Boyd (2024-08-19 16:36:26)
> The QUPs aren't shared in a way that requires parking the RCG at an
> always on parent in case some other entity turns on the clk. The
> hardware is capable of setting a new frequency itself with the DFS mode,
> so parking is unnecessary. Furthermore, there aren't any GDSCs for these
> devices, so there isn't a possibility of the GDSC turning on the clks
> for housekeeping purposes.
>
> This wasn't a problem to mark these clks shared until we started parking
> shared RCGs at clk registration time in commit 01a0a6cc8cfd ("clk: qcom:
> Park shared RCGs upon registration"). Parking at init is actually
> harmful to the UART when earlycon is used. If the device is pumping out
> data while the frequency changes you'll see garbage on the serial
> console until the driver can probe and actually set a proper frequency.
>
> Revert the QUP part of commit 929c75d57566 ("clk: qcom: gcc-sm8550: Mark
> RCGs shared where applicable") so that the QUPs don't get parked during
> clk registration and break UART operations.
>
> Fixes: 01a0a6cc8cfd ("clk: qcom: Park shared RCGs upon registration")
> Fixes: 929c75d57566 ("clk: qcom: gcc-sm8550: Mark RCGs shared where applicable")
> Cc: Konrad Dybcio <konradybcio@...nel.org>
> Cc: Bjorn Andersson <andersson@...nel.org>
> Cc: Taniya Das <quic_tdas@...cinc.com>
> Reported-by: Amit Pundir <amit.pundir@...aro.org>
> Closes: https://lore.kernel.org/CAMi1Hd1KQBE4kKUdAn8E5FV+BiKzuv+8FoyWQrrTHPDoYTuhgA@mail.gmail.com
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---

Applied to clk-fixes