[PATCH v3 2/2] drm: bridge/dw_hdmi: add dw hdmi i2c bus adapter support

Russell King - ARM Linux linux at arm.linux.org.uk
Wed Sep 16 15:18:19 PDT 2015

On Wed, Sep 16, 2015 at 02:56:57PM -0700, Doug Anderson wrote:
> Yes, I'd expect 100kHz and 400kHz.
> I agree that 50ms is non-trivial, but it's also not something you're
> doing lots of.  I'd expect that the EDID is read over this channel at
> cable plugin time and then not used much after that.  Adding an extra
> 40ms (10ms vs 50ms) before we can access the TV doesn't seem terrible
> for compatibility.
> Doing a quick scan for what others in mainline do:
> A few can be found with:
> $ git grep -A3 hdmiddc | grep clock-freq
> arch/arm/boot/dts/stihxxx-b2120.dtsi-
> clock-frequency = <100000>;
> arch/arm/boot/dts/tegra30-apalis.dtsi-          clock-frequency = <100000>;
> arch/arm/boot/dts/tegra30-beaver.dts-           clock-frequency = <100000>;
> arch/arm/boot/dts/tegra30-colibri.dtsi-         clock-frequency = <100000>;

This is a sure way to propagate a bug.

I said in a previous email that you need to check the HDMI and CEA
specs.  I've done this, and HDMI 1.3a specifies a maximum SCL clock
rate of 100kHz.

So that's settled then.  100kHz is must be.  Using 400kHz is out of

FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

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