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

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Message-ID: <CAL_JsqLN5veD9QHMmEqX5mmX+iHM69O=o+KFauej1QdqEpyUhw@mail.gmail.com>
Date:   Thu, 10 Nov 2016 11:40:35 -0600
From:   Rob Herring <robh@...nel.org>
To:     Joel Stanley <joel@....id.au>
Cc:     Andrew Jeffery <andrew@...id.au>, Lee Jones <lee.jones@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...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 Wed, Nov 9, 2016 at 9:19 PM, Joel Stanley <joel@....id.au> wrote:
> 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

Okay.

>>> +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?

Right.

Acked-by: Rob Herring <robh@...nel.org>

Rob