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

Andy Green
2012-06-28T12:16:07Z

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
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