linux-kernel - Re: [PATCH v2 2/6] mfd: dt: Add bindings for the Aspeed SoC Display Controller (GFX)

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Date:   Thu, 10 Nov 2016 13:49:05 +1030
From:   Joel Stanley <joel@....id.au>
To:     Rob Herring <robh@...nel.org>, Andrew Jeffery <andrew@...id.au>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 2/6] mfd: dt: Add bindings for the Aspeed SoC Display
 Controller (GFX)

On Thu, Nov 10, 2016 at 4:56 AM, Rob Herring <robh@...nel.org> wrote:
> On Thu, Nov 03, 2016 at 01:07:57AM +1030, Andrew Jeffery wrote:
>> The Aspeed SoC Display Controller is presented as a syscon device to
>> arbitrate access by display and pinmux drivers. Video pinmux
>> configuration on fifth generation SoCs depends on bits in both the
>> System Control Unit and the Display Controller.
>>
>> Signed-off-by: Andrew Jeffery <andrew@...id.au>
>> ---
>>  Documentation/devicetree/bindings/mfd/aspeed-gfx.txt | 17 +++++++++++++++++
>
> The register space can't be split to 2 nodes?

Do you mean splitting the GFX IP and enable register into two nodes?

We can't. Pinmux needs to check bit 6 and 7 in GFX064, which is in the
middle the IP block:

GFX060: CRT Control Register I
GFX064: CRT Control Register II
GFX068: CRT Status Register
GFX06C: CRT Misc Setting Register

>> +The Aspeed SoC Display Controller primarily does as its name suggests, but also
>> +participates in pinmux requests on the g5 SoCs. It is therefore considered a
>> +syscon device.
>> +
>> +Required properties:
>> +- compatible:                "aspeed,ast2500-gfx", "syscon"
>
> I think perhaps we should drop the syscon here and the driver should
> just register as a syscon.

We want the regmap to be present whenever the GFX driver or pinmux is
loaded. If we register it in pinmux but chose to not build in that
driver, we lack the regmap. Same for the case where a user builds in
the GFX driver and not pinmux. I think this means we want the syscon
compatible string, unless my understanding is wrong?

Cheers,

Joel