From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Wed, 16 Sep 2015 23:18:19 +0100 Subject: [PATCH v3 2/2] drm: bridge/dw_hdmi: add dw hdmi i2c bus adapter support In-Reply-To: References: <1440970470-7155-1-git-send-email-vladimir_zapolskiy@mentor.com> <55F9D7F0.4070402@mentor.com> Message-ID: <20150916221819.GJ21084@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 specification. -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.