Re: [PATCH 0/2] drm/tilcdc drm/i2c/tda998x workaround for sync issues on TI SoC

[Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>]

On 07/25/2013 09:32 PM, Rob Clark wrote:
> On Thu, Jul 25, 2013 at 2:32 PM, Darren Etheridge <detheridge@ti.com> wrote:
>> Russell King and Sebastian Hasselbarth had proposed some very good changes
>> for the tda998x HDMI encoder driver.  But when those changes were tested
>> on BeagleBone Black against the tilcdc driver many modes would no longer
>> display correctly.  After analyzing the sync signals from the TI lcd contoller
>> to the nxp it is apparent that the hsync/vsync's are not rising at the same
>> time as per the VESA spec and this is causing the HDMI encoder to get
>> messed up and failing to lock correctly.
>>
>> This series of patches should be applied on top of:
>>
>> Russell King's
>> rmk's Dove DRM/TDA19988 Cubox driver series
>>
>> Sebastian Hasselbarth's
>> drm/i2c: tda998x: fix sync generation and calculation
>>
>> I have done as much of the change as I can in the tilcdc driver but there
>> is a small unavoidable change in the tda998x driver.  However I have been
>> careful not to break anything from the Dove drivers perspective. It
>> would be great if somebody can test on Cubox and confirm that.
>>
>> This patch set inverts the hsync signal coming from the tilcdc so the NXP
>> is kept happy and then shifts the output to the right to compensate for the
>> sync timing issues.  Display modes from the NXP have been verified using a
>> HDMI analyzer and are reporting correct timings at the output stage.
>>
>> Hopefully this will allow the dove/tda driver changes to progress now that
>> were blocked as per this discussion:
>> http://lists.freedesktop.org/archives/dri-devel/2013-July/040900.html
>>
>
> Good find Darren!  The patches look good to me from a quick review.
> It would be good to get a tested-by from someone on cubox, but it is
> good that we finally found the issue so that we can unblock further
> tda998x development.

Thanks to Darren, I can now test tda998x sync changes on both Cubox and
Beaglebone Black. I don't think the changes will affect Armada DRM in
any way, as it is not setting adjusted_mode.

I will put a scope on AM335x/TDA998x sync signals to fully understand
the issues tilcdc has, but I can think of a flag for TDA998x to always
accept falling input hsync/vsync and tilcdc to supply that sync. That
will maybe allow us to get rid of hskew workaround.

As far as I understand the issue, tilcdc always aligns VS with the
rising HS edge? If so, enforcing positive HS/VS on tilcdc and telling
TDA998x that it is always positive, may be a cleaner workaround. TDA998x
can invert input and output sync independently.

In any way, it will take some time to get a working setup. If you are
happy with the patches, I can still send some follow-up patches later.

Sebastian