linux-kernel - Re: [PATCH] arm64: dts: ti: k3-j7200-main: Add McASP nodes

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Message-ID: <20201026145031.ggfugctq65zvgwp2@dismiss>
Date:   Mon, 26 Oct 2020 09:50:31 -0500
From:   Nishanth Menon <nm@...com>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
CC:     <t-kristo@...com>, <devicetree@...r.kernel.org>,
        <robh+dt@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: dts: ti: k3-j7200-main: Add McASP nodes

Peter,

On 13:38-20201007, Peter Ujfalusi wrote:
[...]
> >>>> +		status = "disabled";
> >>>
> >>> I see that there is inconsistent usage of "disabled" in our SoC.dts
> >>>
> >>> Our generic rule has been set them to disabled in board.dtsi
> >>> McASP and DSS for existing SoC dts do not follow this.. which is a tad
> >>> confusing.. (considering that not even all uarts come out on every board
> >>> and every uart needs pinmux to function..)
> >>
> >> "keep them disabled because several required properties are not present
> >> as they are board specific."
> >>
> >> In board file the enabled mcasp must be updated with options that is
> >> required for operation. Without those option the McASP can not be
> >> initialized.
> >>
> >> I think we have been revisiting the very same discussion every time we
> >> have a new SoC with McASP...
> >>
> > 
> > Yep.. This doe'snt really follow the rest of the SoC definition. [1]
> > came to mind. The McASP discussion is a variation in the debate of the
> > same.
> 
> Right, saying status = "okay" to a node which is missing required
> properties (which can only be added by boards when the McASP is
> connected up) does not sound a good solution.
> How should the SW handle that? Fail the device probe and return with
> -EINVAL or eat up the error and just probe with broken configuration.
> Since the peripheral is not used, the broken configuration will not
> cause much runtime errors as there will be no runtime use of the peripheral.
> 
> status of fail or fail-sss is not a good one either, their definition is:
> "Indicates that the device is not operational. A serious error was
> detected in the device, and it is unlikely to become operational without
> repair."
> 
> The peripheral is fine, we are just trying to enable it without
> providing the needed properties.
> 
> > I'd argue Serdes, or for that matter any IP that has a link to
> > outside-the-SoC world has the same discussion point.
> 
> status = "disabled" is still the closest thing for everything which have
> external dependencies. There is not much point to enable an i2c bus
> without making sure that the signals are actually routed to the pins
> where they supposed to go.
> 
> Or from other pow: a board design is not based on what is _not_
> connected to outside world, but you actually _connect_ or _enable_
> certain peripherals to external components, connectors.

OK, I will buy the argument that the current status thingy is a bit
overloaded and does'nt imply the correct state we need it to imply with
"fail-sss" either - I remember an argument for "fail-incomplete", but
that never happened anyways.

Lets add this argument to the commit message and repost after testing
on 5.10-rc1 please?

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D