[Intel-gfx] [PATCH] drm/i915: Delete the strict EDID check for SDVO DVI-D monitor

ykzhao yakui.zhao at intel.com
Fri Oct 23 03:42:57 CEST 2009

On Thu, 2009-10-22 at 23:18 +0800, Eric Anholt wrote:
> On Thu, 2009-10-22 at 17:41 +0800, ykzhao wrote:
> > On Thu, 2009-10-22 at 15:15 +0800, Keith Packard wrote:
> > > Excerpts from yakui.zhao's message of Thu Oct 22 14:25:33 +0900 2009:
> > > > From: Zhao Yakui <yakui.zhao at intel.com>
> > > > 
> > > > In theory we can use EDID obtained from the DVI-D monitor to detect whether
> > > > the device is connected or not.
> > > 
> > > The DVI spec *requires* EDID on DVI-D monitors. Do we have any
> > > information on why this is failing? Perhaps our EDID code is broken
> > > for some monitors?
> > This issue happens on one SDVO card with multiple inputs and multiple
> > outputs.
> > 
> > At first IMO maybe this is related with the incorrect DDC bus behind
> > SDVO card. I write a debug patch which tries to read 128byte by using
> > different DDC bus.(PROM, DDC1, DDC2, DDC3).
> > Unfortunately it can read nothing even when the different DDC bus is
> > used. It always reports that there doesn't exist the 0xA0 slave address.
> > 
> > But one bug reporter can read the EDID by using the
> > read-edid-tool(1.4.2), which is realized by using BIOS call. 
> > 
> > It is very interesting. Maybe our I2C bus code is different with that
> > used in Video-BIOS.
> If the chipset/monitor combo is capable of reading an EDID, we need to
> fix the fact that our code is failing at reading the EDID rather than
> disabling our EDID use.
   I will look at this issue. In fact when looking at the vbios code it
seems that the GMBUS is used to do the I2C transaction. But our code
always uses the GPIO to do the I2C transaction. I am not sure whether
this issue is related with the I2C bus.
If we switch the I2C bus code from GPIO to GMBUS, it will take long time
to finish. At the same time we will have to test whether it can work on
most boxes.(Include: 855, 915, 945, 965, G45 and so on).
In fact this issue is only related with the SDVO DDC bus. I am not sure
whether it is worth spending so much time on it.

Now my patch is only to workaround the issue so that the boxes can be
booted correctly as what we have done.


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