Hi Tony, Roger, I recently raised the i2c issue with reading EDID from a DVI monitor on Panda, when booting with DT. I just couldn't get reading EDID work at all reliably. I now see problems with non-DT also. Booting with 3.10-rc5, with DSS compiled into the kernel, reading EDID fails during the boot. I can later read the EDID fine from userspace. With help from Roger, we found the issue. DVI cable has a +5V line, that the source (i.e. Panda) has to provide. This +5V is required to read EDID, but according to the documentation I think it's actually required to show video also (although I guess this could depend on the monitor). I think for OMAP3 boards the +5V is always-on (I haven't looked at OMAP3 boards yet, though). For Panda, the +5V comes from DC_HST_5V, controlled with a GPIO, which is used for USB and currently managed by USB in arch/arm/mach-omap2/usb-host.c, which creates a fixed voltage hsusbX_vcc regulator. So, basically, if USB is disabled, DVI doesn't work. This is why I see problems with DT (no USB), and non-DT (USB enabled after DVI is enabled). To fix this properly I need to add regulator handling to the DVI driver, and we need to share the same supply with USB and DVI. However, while the above shouldn't be particularly difficult, it's still not simple. And additional complications come with DT boot, as DSS doesn't support DT yet. We have the hack that enables DSS for Panda and SDP board when booting with DT, but I don't think it's possible to manage the shared regulator easily in that setup (ie. USB and the regulator being described in DT, DSS and DVI added the old way in dss-common.c). So I think the simplest solution is to make DC_HST_5V always-on. This should be fixed for 3.10 also. Any idea if DC_HST_5V is a big power sink if it's always enabled? If it's a big one, I could look at how to hack the DVI driver so that it would find the regulator. I'm quite sure I won't be neat, though. Tomi
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