Re: [PATCH 3/3] OMAPDSS: HDMI: Cache EDID

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On 06/28/12 19:38, the mail apparently from Tomi Valkeinen included:
On Thu, 2012-06-28 at 14:10 +0300, Tomi Valkeinen wrote:
On Thu, 2012-06-28 at 16:28 +0530, Jassi Brar wrote:

Sorry a correction. Reading detect() won't work. I suggest we keep HPD
IRQ enabled for the lifetime of the driver.

Ok, I see. But that's not acceptable. It would require us to keep the
TPD12S015 always powered and enabled. Even if you're not interested in
using HDMI at all.

Btw, a bigger problem that I see is how we have to do read_edid() (and
detect(), if I recall correctly): we enable the whole video pipeline and
output. We should only enable enough of the HW to be able to read the
EDID or read the HPD GPIO.

I've noticed that this leads to sync losts quite easily, as we switch
the hdmi output on and off quickly multiple times. I couldn't figure out
why the sync losts happen though, and I did try quite many different
combinations how to handle it.

SYNC LOST is one evil lurking in there, the other evil is EDID fetch "operation stopped" error. We were unable to figure out what was trampling on what there without the SoC HDMI PHY IP data which we don't have.

Also at the moment I think we depower / repower the internal SoC and external PHY chip more than we need. Each time we remove the HDMI link power, after a short time where the big capacitor at the charge pump output decays enough (a time dependent on exact details of load presented by the TV or monitor...), hpd from the monitor goes low and remains there until we power the charge pump again. In turn the new hpd recognition provokes a new edid fetch. Something about that sequence provokes the "operation stopped" on EDID fetch, with Jassi's patches we manage to avoid it.

Removing that syndrome, and just not enabling and disabling stuff like SoC HDMI PHY willy nilly can maybe be something else targeted by this proposed 4-state power scheme.

-Andy

--
Andy Green | TI Landing Team Leader
Linaro.org │ Open source software for ARM SoCs | Follow Linaro
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