linux-kernel - Re: [PATCH v5 1/5] dt-bindings: gpu: add bindings for the ARM Mali Midgard GPU

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Date:   Fri, 14 Jul 2017 07:41:24 +0100
From:   Guillaume Tucker <guillaume.tucker@...labora.com>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Heiko Stübner <heiko@...ech.de>,
        Neil Armstrong <narmstrong@...libre.com>,
        devicetree@...r.kernel.org,
        Sjoerd Simons <sjoerd.simons@...labora.com>,
        Wookey <wookey@...kware.org>, linux-kernel@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        John Reitan <john.reitan@....com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 1/5] dt-bindings: gpu: add bindings for the ARM Mali
 Midgard GPU

Hi Brian,

On 12/07/17 18:26, Brian Norris wrote:
> Hi Guillaume,
>
> I know this has already been merged, but I figured here was an OK place
> to note (inline):
>
> On Wed, May 03, 2017 at 10:56:25AM +0100, Guillaume Tucker wrote:

[...]

>> diff --git a/Documentation/devicetree/bindings/gpu/arm,mali-midgard.txt b/Documentation/devicetree/bindings/gpu/arm,mali-midgard.txt
>> new file mode 100644
>> index 000000000000..d3b6e1a4713a
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/gpu/arm,mali-midgard.txt
>
> ^^ This file name implies we're talking about a base "arm,mali-midgard"
> compatible property.
>
>> @@ -0,0 +1,86 @@
>> +ARM Mali Midgard GPU
>> +====================
>> +
>> +Required properties:
>> +
>> +- compatible :
>> +  * Must contain one of the following:
>> +    + "arm,mali-t604"
>> +    + "arm,mali-t624"
>> +    + "arm,mali-t628"
>> +    + "arm,mali-t720"
>> +    + "arm,mali-t760"
>> +    + "arm,mali-t820"
>> +    + "arm,mali-t830"
>> +    + "arm,mali-t860"
>> +    + "arm,mali-t880"
>> +  * which must be preceded by one of the following vendor specifics:
>> +    + "amlogic,meson-gxm-mali"
>> +    + "rockchip,rk3288-mali"
>
> But it's not listed here.
>
>> +
>> +- reg : Physical base address of the device and length of the register area.
>> +
>> +- interrupts : Contains the three IRQ lines required by Mali Midgard devices.
>> +
>> +- interrupt-names : Contains the names of IRQ resources in the order they were
>> +  provided in the interrupts property. Must contain: "job", "mmu", "gpu".
>> +
>> +
>> +Optional properties:
>> +
>> +- clocks : Phandle to clock for the Mali Midgard device.
>> +
>> +- mali-supply : Phandle to regulator for the Mali device. Refer to
>> +  Documentation/devicetree/bindings/regulator/regulator.txt for details.
>> +
>> +- operating-points-v2 : Refer to Documentation/devicetree/bindings/power/opp.txt
>> +  for details.
>> +
>> +
>> +Example for a Mali-T760:
>> +
>> +gpu@...30000 {
>> +	compatible = "rockchip,rk3288-mali", "arm,mali-t760", "arm,mali-midgard";
>
> And it *is* used here in this example.
>
> So, should it be used/documented or not?

The important part is that having only arm,mali-midgard in the
gpu node is not enough to accurately describe the hardware, which
is why it is not listed in the required compatible strings.  On
the other hand, it does help with describing the hardware, so
it's fine to use it.  If people find this confusing then I guess
we could add something to say that arm,mali-midgard can be used
optionally in addition to the specific ones.

Also, if you look at the 64-bit ARM CPUs for example, they
typically have armv8 in their node although armv8 is not
mentioned anywhere in the bindings documentation...

Guillaume