linux-kernel - Re: [PATCH 1/7] arm64: dts: imx8-ss-lsio: fix pwm lpcg indices

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Date: Tue, 2 Apr 2024 11:09:17 -0400
From: Frank Li <Frank.li@....com>
To: Fabio Estevam <festevam@...il.com>
Cc: Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	NXP Linux Team <linux-imx@....com>,
	Marcel Ziswiler <marcel.ziswiler@...adex.com>,
	Philippe Schenker <philippe.schenker@...adex.com>,
	Max Krummenacher <max.krummenacher@...adex.com>,
	Alexander Stein <alexander.stein@...tq-group.com>,
	Joakim Zhang <qiangqing.zhang@....com>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH 1/7] arm64: dts: imx8-ss-lsio: fix pwm lpcg indices

On Mon, Apr 01, 2024 at 08:04:56PM -0300, Fabio Estevam wrote:
> On Mon, Apr 1, 2024 at 7:25 PM Frank Li <Frank.Li@....com> wrote:
> >
> > lpcg's arg0 should use clock indices instead of index.
> >
> > pwm0_lpcg: clock-controller@...00000 {
> >         ...                                                // Col1  Col2
> >         clocks = <&clk IMX_SC_R_PWM_0 IMX_SC_PM_CLK_PER>,  // 0     0
> >                  <&clk IMX_SC_R_PWM_0 IMX_SC_PM_CLK_PER>,  // 1     1
> >                  <&clk IMX_SC_R_PWM_0 IMX_SC_PM_CLK_PER>,  // 2     4
> >                  <&lsio_bus_clk>,                          // 3     5
> >                  <&clk IMX_SC_R_PWM_0 IMX_SC_PM_CLK_PER>;  // 4     6
> >         clock-indices = <IMX_LPCG_CLK_0>, <IMX_LPCG_CLK_1>,
> >                         <IMX_LPCG_CLK_4>, <IMX_LPCG_CLK_5>,
> >                         <IMX_LPCG_CLK_6>;
> > };
> >
> > Col1: index, which exited dts try to get.
> 
> I cannot understand this sentence, sorry.

This base on downstream dts code.  Downstream code use index in 'Col1' to
get clock.

For example:
<&pwm0_lpcg 3> means &lsio_bus_clk.

When someone do upstream, miss understand or omit upsteam lpcg driver's
difference between downstream and upstream version. And it also work even
index is wrong.

I realize this problem when I try to enable audio device for qm. The
difference cause audio can't work.  The grep lpcg [0-9] to find this
problem.

> 
> > Col2: actual index in lpcg driver.
> 
> You should not describe DT in terms of Linux driver.

It just descript the actual hehavior in current drivers to explain why it
can work even arg0 is wrong.


for example: <&pwm0_lpcg 4>, developer intent to get 
	<&clk IMX_SC_R_PWM_0 IMX_SC_PM_CLK_PER>;  // 4     6

but lpcg driver device device arg0 (4) by 4, get 1. So below clock return
	<&clk IMX_SC_R_PWM_0 IMX_SC_PM_CLK_PER>,  // 1     1 

Both it is IMX_SC_PM_CLK_PER, so pwm works luckly.

But correct code should be <&pwm0_lpcg IMX_LPCG_CLK_6>. 


Frank