linux-kernel - Re: [PATCH 1/3] dt-bindings: spi: Update clocks property for ARM pl022

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Message-ID: <1763f668-2582-c05e-7ac8-d635bc84ef82@arm.com>
Date:   Mon, 28 Feb 2022 15:27:08 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Kuldeep Singh <singh.kuldeep87k@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-spi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 1/3] dt-bindings: spi: Update clocks property for ARM
 pl022

On 2022-02-28 15:11, Mark Brown wrote:
> On Mon, Feb 28, 2022 at 02:26:12PM +0000, Robin Murphy wrote:
> 
>> Who says that minItems is missing? Looking at the PL022 TRM[1] it seems
>> clear that SSPCLK is pretty fundamental to useful operation. If that DT ever
>> worked, it must be that the same clock is wired to both inputs, and the fact
>> that that's how the neighbouring PL011 is described is strongly suggestive.
> 
> Well, it could also be that the clock is wired to some other clock which
> is always on (which I guess is why the driver allows this in the first
> place, there's a lot of sloppy code around stuff like that in the tree).

I wouldn't say the driver "allows" it, so much as it just blindly grabs 
the first clock assuming it's SSPCLK per the binding, and thus it will 
happen to work out if the underlying physical clock is the same as, or 
equivalent to, the APB PCLK. Otherwise, it's already into some degree of 
not working properly, by virtue of reading the wrong clock rate.

Robin.