linux-kernel - Re: [PATCH] ARM: dts: ti/omap: gta04: fix pm issues caused by spi module

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Message-ID: <20241108184118.5ee8114c@akair>
Date: Fri, 8 Nov 2024 18:41:18 +0100
From: Andreas Kemnade <andreas@...nade.info>
To: Roger Quadros <rogerq@...nel.org>
Cc: tony@...mide.com, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, hns@...delico.com, linux-omap@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 aaro.koskinen@....fi, khilman@...libre.com, stable@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: ti/omap: gta04: fix pm issues caused by spi
 module

Am Fri, 8 Nov 2024 14:42:14 +0200
schrieb Roger Quadros <rogerq@...nel.org>:

> > diff --git a/arch/arm/boot/dts/ti/omap/omap3-gta04.dtsi b/arch/arm/boot/dts/ti/omap/omap3-gta04.dtsi
> > index 3661340009e7a..11f8af34498b1 100644
> > --- a/arch/arm/boot/dts/ti/omap/omap3-gta04.dtsi
> > +++ b/arch/arm/boot/dts/ti/omap/omap3-gta04.dtsi
> > @@ -612,19 +612,23 @@ &i2c3 {
> >  };
> >  
> >  &mcspi1 {
> > -	status = "disabled";  
> 
> But according to commit a622310f7f01 ("ARM: dts: gta04: fix excess dma channel usage"),
> these mcspi modules are not used. So it doesn't make sense to enable them even if it
> seems to solve the power management issue?
> 
They are not used, if they are just disabled, kernel does not touch
them, so if it is there, the kernel can handle
pm. At least as long as it is not under ti,sysc.

There are probably cleaner solutions for this, but for a CC: stable I
would prefer something less invasive.

I can try a ti-sysc based fix in parallel.

> Does bootloader leave the mcspi modules in a unwanted state?

Or at least something related to them. 
As said, for the blamed patch I checked only for CM_IDLEST1_CORE
and CM_FCLKEN1_CORE.

> Would it make sense for the bus driver to explicitly turn off all modules?

Hmm, not very clear what you mean. AFAIK everything below ti-sysc gets
turned off if a disable is in the child node. Explicitly disabling such
stuff in the dtsi and enable it in the board dts sound sane
to me at first glance. I think it is a common pattern. The question is
whether that causes confusion with not ti-sysc stuff. Well, having
status=okay everywhere in the dts should not harm.
But as said for a regression fix some overhaul affecting every device 
is out of scope.

Regards,
Andreas