linux-kernel - Re: [PATCH v2 06/13] drm/sun4i: hdmi: Allow using second PLL as TMDS clk parent

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Date:   Tue, 26 Sep 2017 11:58:38 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Mark Brown <broonie@...nel.org>, David Airlie <airlied@...ux.ie>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH v2 06/13] drm/sun4i: hdmi: Allow using second PLL as TMDS
 clk parent

On Tue, Sep 26, 2017 at 06:59:12AM +0000, Chen-Yu Tsai wrote:
> Allwinner SoCs typically have two PLLs reserved for video related usage.
> At the moment we only support using the first one to feed the HDMI
> transmitter block's TMDS clock.
> 
> Let the HDMI encoder's TMDS clock go through all of its parents when
> calculating possible clock rates. This allows usage of the second video
> PLL as its parent.
> 
> Note that this does not handle conflicting pixel clocks. It is entirely
> possible to have an LCD panel use one pixel clock rate, only to be
> overridden by the HDMI transmitter's clock rate request when the second
> display pipeline is enabled.
> 
> This should be handled by having all the clock drivers honor clock rate
> ranges, and have the consumers use clk_set_rate_min/clk_set_rate_max.

That, or relying on clk_set_rate_protect

Acked-by: Maxime Ripard <maxime.ripard@...e-electrons.com>

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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