linux-kernel - Re: [PATCH v2 2/2] ARM: dts: da850-lcdk: specify the maximum pixel clock rate for tilcdc

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Message-ID: <4f2a02c4-062f-6faf-1024-2a8718a9701f@ti.com>
Date:   Tue, 29 Nov 2016 16:23:23 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Russell King <linux@...linux.org.uk>
CC:     LKML <linux-kernel@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        linux-drm <dri-devel@...ts.freedesktop.org>,
        linux-devicetree <devicetree@...r.kernel.org>,
        Jyri Sarha <jsarha@...com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        David Airlie <airlied@...ux.ie>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v2 2/2] ARM: dts: da850-lcdk: specify the maximum pixel
 clock rate for tilcdc

On Monday 28 November 2016 05:45 PM, Bartosz Golaszewski wrote:
> Due to memory throughput constraints any display mode for which the
> pixel clock rate exceeds the recommended value of 37500 KHz must be
> filtered out.

I think there might be more reasons than memory throughput constraints
for the reasoning behind 37.5Mhz cap on pixel clock. Why not just refer
to the datasheet section that places this constraint so we know its a
hardware restriction.

> 
> Specify the max-pixelclock property for the display node for
> da850-lcdk.
> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> ---
>  arch/arm/boot/dts/da850-lcdk.dts | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/boot/dts/da850-lcdk.dts b/arch/arm/boot/dts/da850-lcdk.dts
> index d864f11..1283263 100644
> --- a/arch/arm/boot/dts/da850-lcdk.dts
> +++ b/arch/arm/boot/dts/da850-lcdk.dts
> @@ -285,6 +285,7 @@
>  
>  &display {
>  	status = "okay";
> +	max-pixelclock = <37500>;

Should this not be in da850.dtsi since its an SoC imposed constraint? If
a board needs narrower constraint, it can override it. But I guess most
well designed boards will just hit the SoC constraint.

Thanks,
Sekhar