linux-kernel - Re: [PATCH v3 1/2] clk: qcom: dispcc-sc7180: Only park display clks at init

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Message-ID: <ZtB-lZWdRIv3mLFr@hovoldconsulting.com>
Date: Thu, 29 Aug 2024 15:58:45 +0200
From: Johan Hovold <johan@...nel.org>
To: Stephen Boyd <swboyd@...omium.org>
Cc: Konrad Dybcio <konradybcio@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, patches@...ts.linux.dev,
	linux-clk@...r.kernel.org,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Amit Pundir <amit.pundir@...aro.org>,
	Taniya Das <quic_tdas@...cinc.com>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Subject: Re: [PATCH v3 1/2] clk: qcom: dispcc-sc7180: Only park display clks
 at init

On Wed, Aug 28, 2024 at 10:17:07AM -0700, Stephen Boyd wrote:
> Amit Pundir reports that audio and USB-C host mode stops working on
> sm8550 after commit 01a0a6cc8cfd ("clk: qcom: Park shared RCGs upon
> registration"). That's because the gcc_usb30_prim_master_clk_src clk is
> registered and clk_rcg2_shared_init() parks it on XO. Running USB at a
> slower speed than the link supports is effectively under-clocking the
> USB link and probably confusing the downstream USB devices.
> 
> We didn't need to change all the shared RCGs to park on XO at
> registration time in commit commit 01a0a6cc8cfd ("clk: qcom: Park shared
> RCGs upon registration"). Instead, we only needed to park the few
> display related clks on sc7180 to fix the issue.
> 
> Fix sm8550 (and likely other qcom SoCs) by skipping the parking part of
> clk_rcg2_shared_init(). Make that the default init clk_op for shared
> RCGs, but keep the part where we cache the config register as that's
> still necessary to figure out the true parent of the clk is. Introduce
> another set of clk_ops 'clk_rcg2_shared_init_park' that does what
> clk_rcg2_shared_init() was doing and use that for the display clks on
> sc7180. This fixes the sm8550 problem and limits the "park upon
> registration" logic to the display clks that need it.
> 
> Fixes: 01a0a6cc8cfd ("clk: qcom: Park shared RCGs upon registration")
> Cc: Konrad Dybcio <konradybcio@...nel.org>
> Cc: Bjorn Andersson <andersson@...nel.org>
> Cc: Taniya Das <quic_tdas@...cinc.com>
> Cc: Neil Armstrong <neil.armstrong@...aro.org>
> 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>

I can confirm that this fixes the earlycon issue on x1e80100 that Bryan
reported here:

	https://lore.kernel.org/lkml/20240823-x1e80100-clk-fix-v1-1-0b1b4f5a96e8@linaro.org/

Perhaps you can drop the "dispcc-sc7180:" prefix from Subject when
applying (or resending) since this fixes a regression on multiple
Qualcomm SoCs. For example, use something like:

	clk: qcom: Only park sc7180 display clks at init

Tested-by: Johan Hovold <johan+linaro@...nel.org>

Johan