linux-kernel - Re: [PATCH] ARM: dts: Set status to disable for MMC3

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Message-ID: <20191007165859.GV5610@atomide.com>
Date:   Mon, 7 Oct 2019 09:58:59 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Emmanuel Vadot <manu@...ouilliste.com>
Cc:     Emmanuel Vadot <manu@...ebsd.org>, bcousson@...libre.com,
        robh+dt@...nel.org, mark.rutland@....com,
        linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: Set status to disable for MMC3

* Emmanuel Vadot <manu@...ouilliste.com> [191007 16:39]:
> On Mon, 7 Oct 2019 09:16:34 -0700
> Tony Lindgren <tony@...mide.com> wrote:
> 
> > Hi,
> > 
> > * Emmanuel Vadot <manu@...ebsd.org> [191007 08:04]:
> > > Commit 5b63fb90adb95 ("ARM: dts: Fix incomplete dts data for am3 and am4 mmc")
> > > fixed the mmc instances on the l3 interconnect but removed the disabled status.
> > > Fix this and let boards properly define it if it have it.
> > 
> > The dts default is "okay", and should be fine for all the
> > internal devices even if not pinned out on the board. This
> > way the devices get properly idled during boot, and we
> > avoid repeating status = "enabled" over and over again in
> > the board specific dts files.
> 
>  That is not correct, if a status != "disabled" then pinmuxing will be
> configured for this device and if multiple devices share the same pin
> then you have a problem. Note that I have (almost) no knowledge on Ti
> SoC but I doubt that this is not the case on them.

Hmm well, that should not be needed. The pinmux configuration is always
done in a board specific dts file.

>  Also every other boards that I work with use the standard of setting
> every node to disabled in the dtsi and let the board enable them at
> will. Is there something different happening in the TI world ?

There should be no need to do that for SoC internal devices, the
the default status = "okay" should be just fine. Setting the
status = "disabled" for SoC internal devices and then enabling them
again for tens of board specific dts files just generates tons of
pointless extra churn for the board specific configuration.

> > Then the board specific dts files might want to configure
> > devices with status = "disabled" if really needed. But this
> > should be only done for devices that Linux must not use,
> > such as crypto acclerators on secure devices if claimed by
> > the secure mode.
> > 
> > So if this fixes something, it's almost certainly a sign
> > of something else being broken?
> 
>  In this case it's FreeBSD being  because (I think) we have bad support
> for the clocks for this module so we panic when we read from it as the
> module isn't clocked. And since I find it wrong to have device enabled
> while it isn't present I've sent this patch.

Thanks for clarifying what happens. OK, sounds like FreeBSD might be
missing clock handling for some devices then.

What Linux does is probe the internal devices and then idle the
unused ones as bootloaders often leave many things enabled. Otherwise
the SoC power management won't work properly because device clocks
will block deeper SoC idle states.

Regards,

Tony

> > > Fixes: 5b63fb90adb95 ("ARM: dts: Fix incomplete dts data for am3 and am4 mmc")
> > > Signed-off-by: Emmanuel Vadot <manu@...ebsd.org>
> > > ---
> > >  arch/arm/boot/dts/am33xx.dtsi | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/arch/arm/boot/dts/am33xx.dtsi b/arch/arm/boot/dts/am33xx.dtsi
> > > index fb6b8aa12cc5..b3a1fd9e39fa 100644
> > > --- a/arch/arm/boot/dts/am33xx.dtsi
> > > +++ b/arch/arm/boot/dts/am33xx.dtsi
> > > @@ -260,6 +260,7 @@
> > >  				ti,needs-special-reset;
> > >  				interrupts = <29>;
> > >  				reg = <0x0 0x1000>;
> > > +				status = "disabled";
> > >  			};
> > >  		};
> > >  
> > > -- 
> > > 2.22.0
> > > 
> 
> 
> -- 
> Emmanuel Vadot <manu@...ouilliste.com>