linux-kernel - Re: [PATCH v2 4/8] drm/fsl-dcu: add extra clock for pixel clock

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Date:	Thu, 31 Mar 2016 09:42:09 -0500
From:	Rob Herring <robh@...nel.org>
To:	Stefan Agner <stefan@...er.ch>
Cc:	dri-devel@...ts.freedesktop.org, shawnguo@...nel.org,
	kernel@...gutronix.de, airlied@...ux.ie, daniel.vetter@...ll.ch,
	jianwei.wang.chn@...il.com, alison.wang@...escale.com,
	meng.yi@....com, alexander.stein@...tec-electronic.com,
	mturquette@...libre.com, sboyd@...eaurora.org,
	mark.rutland@....com, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 4/8] drm/fsl-dcu: add extra clock for pixel clock

On Mon, Mar 28, 2016 at 06:59:58PM -0700, Stefan Agner wrote:
> The Vybrid DCU variant has two independent clock inputs, one
> for the registers (IPG bus clock) and one for the pixel clock.
> Support this distinction in the DCU DRM driver while staying
> backward compatible with devices providing only a single clock
> (e.g. LS1021a SoC's).

I'd suspect that both have 2 clocks, just the LS1021a either didn't 
model the IPG clock or connects both to the same source. The driver 
should support both, but all the dts's should be updated to have 2 
clocks.

> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
>  Documentation/devicetree/bindings/display/fsl,dcu.txt |  4 ++++
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_crtc.c            |  2 +-
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c             | 16 +++++++++++++++-
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h             |  1 +
>  4 files changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/display/fsl,dcu.txt b/Documentation/devicetree/bindings/display/fsl,dcu.txt
> index ebf1be9..f299e1e 100644
> --- a/Documentation/devicetree/bindings/display/fsl,dcu.txt
> +++ b/Documentation/devicetree/bindings/display/fsl,dcu.txt
> @@ -11,6 +11,10 @@ Required properties:
>  - big-endian		Boolean property, LS1021A DCU registers are big-endian.
>  - fsl,panel:		The phandle to panel node.
>  
> +Optional properties:
> +- clocks:		Second handle for pixel clock.
> +- clock-names:		Second name "pix" for pixel clock.

Document these in one place and just add a note that LS1021a only has 1 
clock.

> +
>  Examples:
>  dcu: dcu@...0000 {
>  	compatible = "fsl,ls1021a-dcu";
> diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_crtc.c