linux-kernel - Re: [PATCH] clk: qcom: gcc-sc8280xp: don't use parking clk

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Message-ID: <59429303c8158b146b24d14f4869fcd5.sboyd@kernel.org>
Date: Tue, 03 Sep 2024 13:02:23 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Johan Hovold <johan+linaro@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>, Michael Turquette <mturquette@...libre.com>, linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, Johan Hovold <johan+linaro@...nel.org>
Subject: Re: [PATCH] clk: qcom: gcc-sc8280xp: don't use parking clk_ops for QUPs

Quoting Johan Hovold (2024-09-02 00:08:30)
> A recent change started parking the RCG at an always on parent during
> registration, something which specifically breaks handover from an early
> serial console.
> 
> Quoting Stephen Boyd who fixed this issue for SM8550 [1]:
> 
>         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.
> 
> Fixes: 01a0a6cc8cfd ("clk: qcom: Park shared RCGs upon registration")
> Fixes: d65d005f9a6c ("clk: qcom: add sc8280xp GCC driver")
> Link: https://lore.kernel.org/all/20240819233628.2074654-2-swboyd@chromium.org/ [1]
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---

Applied to clk-fixes