linux-kernel - Re: [PATCH] arm64: dts: imx95: remove CLK

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Message-ID: <aVegAt002L20oBGf@oss.nxp.com>
Date: Fri, 2 Jan 2026 18:37:54 +0800
From: Rain Yang <jiyu.yang@....nxp.com>
To: Marek Vasut <marek.vasut@...lbox.org>
Cc: Frank.Li@....com, conor+dt@...nel.org, devicetree@...r.kernel.org,
	festevam@...il.com, imx@...ts.linux.dev, jiyu.yang@....com,
	kernel@...gutronix.de, krzk+dt@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	liviu.dudau@....com, marek.vasut@...lbox.org, robh@...nel.org,
	s.hauer@...gutronix.de, shawnguo@...nel.org
Subject: Re: [PATCH] arm64: dts: imx95: remove CLK_GPUAPB

On Thu, Jan 01, 2026 at 05:51:12PM +0100, Marek Vasut wrote:
>On 1/1/26 1:37 AM, Rain Yang wrote:
>> On Wed, Dec 31, 2025 at 03:11:21PM +0100, Marek Vasut wrote:
>> > On 12/31/25 4:19 AM, Rain Yang wrote:
>> > > From: Rain Yang <jiyu.yang@....com>
>> > > 
>> > > Dropping CLK_GPUAPB simplifies OPP handling and avoids unnecessary
>> > > complexity.
>> > > 
>> > > Fixes: 67934f248e64 ("arm64: dts: imx95: Describe Mali G310 GPU")
>> > > Signed-off-by: Rain Yang <jiyu.yang@....com>
>> > > ---
>> > >    arch/arm64/boot/dts/freescale/imx95.dtsi | 4 ++--
>> > >    1 file changed, 2 insertions(+), 2 deletions(-)
>> > > 
>> > > diff --git a/arch/arm64/boot/dts/freescale/imx95.dtsi b/arch/arm64/boot/dts/freescale/imx95.dtsi
>> > > index 88bde59e61b2..ab446aa6f73c 100644
>> > > --- a/arch/arm64/boot/dts/freescale/imx95.dtsi
>> > > +++ b/arch/arm64/boot/dts/freescale/imx95.dtsi
>> > > @@ -2164,8 +2164,8 @@ netc_emdio: mdio@0,0 {
>> > >    		gpu: gpu@...00000 {
>> > >    			compatible = "nxp,imx95-mali", "arm,mali-valhall-csf";
>> > >    			reg = <0 0x4d900000 0 0x480000>;
>> > > -			clocks = <&scmi_clk IMX95_CLK_GPU_CGC>, <&scmi_clk IMX95_CLK_GPUAPB>;
>> > > -			clock-names = "core", "coregroup";
>> > > +			clocks = <&scmi_clk IMX95_CLK_GPU_CGC>;
>> > > +			clock-names = "core";
>> > 
>> > I don't think this is correct, SM can disable the GPUAPB clock from the SM
>> > monitor:
>> > 
>> > > $ clock.w gpuapb off
>> > 
>> > Linux has to make sure the GPUAPB clock are enabled to access the GPU
>> > register, hence the clock have to be described in DT.
>> Hi Marek,
>
>Hello Jiyu,
>
>> CLK_GPU and CLK_GPUAPB can only be controlled internally by the SM, not by Linux.
>> CLK_GPUAPB always runs at a fixed frequency, does not require dynamic adjustment,
>> and is practically always on.
>> Additionally, CLK_GPUAPB's frequency is absent from all OPP entries. Removing it
>> could simplify OPP handling logic and reduce unnecessary complexity.
>
>But the SM can turn the GPUAPB clock off, correct ?
>
>Linux has to be able to turn GPUAPB clock on, therefore the GPUAPB clock have
>to be described in DT, correct ?

Yes, CLK_GPUAPB can be turned off by the SM, but by default it remains on, just like
CLK_GPU. AFAIK, there is no scenario where either of these clocks could or would be
disabled in both SM and Linux.

If enabling or disabling CLK_GPUAPB in Linux was wanted, the same shall apply to CLK_GPU
to make this approach reasonable.
Also, OPP framework shall be adjusted to meet these changes too.