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

[Andy Green <andy.green@linaro.org>]

On 06/28/12 19:10, the mail apparently from Tomi Valkeinen included:
> On Thu, 2012-06-28 at 16:28 +0530, Jassi Brar wrote:
>> On 28 June 2012 16:17, Jassi Brar <jaswinder.singh@linaro.org> wrote:
>>> On 28 June 2012 15:44, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
>>>> On Thu, 2012-06-28 at 15:18 +0530, Jassi Brar wrote:
>>>
>>>>>>> --- a/drivers/video/omap2/dss/ti_hdmi_4xxx_ip.c
>>>>>>> +++ b/drivers/video/omap2/dss/ti_hdmi_4xxx_ip.c
>>>>>>> @@ -243,10 +243,13 @@ static int hdmi_check_hpd_state(struct hdmi_ip_data *ip_data)
>>>>>>>
>>>>>>>        hpd = gpio_get_value(ip_data->hpd_gpio);
>>>>>>>
>>>>>>> -     if (hpd)
>>>>>>> +     if (hpd) {
>>>>>>>                r = hdmi_set_phy_pwr(ip_data, HDMI_PHYPWRCMD_TXON);
>>>>>>> -     else
>>>>>>> +     } else {
>>>>>>> +             /* Invalidate EDID Cache */
>>>>>>> +             ip_data->edid_len = 0;
>>>>>>>                r = hdmi_set_phy_pwr(ip_data, HDMI_PHYPWRCMD_LDOON);
>>>>>>> +     }
>>>>>>
>>>>>> There's a problem with this patch, which leaves a wrong EDID in the
>>>>>> cache: if you first have the cable connected and hdmi is enabled, you
>>>>>> then turn off the HDMI display device via sysfs, we do not go to
>>>>>> hdmi_check_hpd_state at all. The next time hdmi is enabled, we only get
>>>>>> the plug-in event, and thus EDID cache is never invalidated.
>>>>>>
>>>>> If the hdmi cable is not replugged during that period, I don't see why
>>>>> would you want the EDID invalidated ?
>>>>
>>>> I wasn't very clear with my comment.
>>>>
>>>> When the display device is disabled, we're not listening to the hpd
>>>> interrupt anymore. So when it's disabled, the cable can be replugged and
>>>> the monitor changed, and the driver won't know about it. And so it'll
>>>> return the old EDID for the new monitor.
>>>>
>>> If that could be a problem, then we already have some problem with
>>> current omapdss.
>>>
>>> I think among the first things, while enabling HDMI, should be to see
>>> if there is really some display connected on the port i.e, HPD
>>> asserted. Only if ti_hdmi_4_detect() returned true, should we
>>> proceed otherwise wait for HPQ irq.
>>>
>>> Unconditionally invalidating edid really seems like a regression - we
>>> impose atleast 50ms (edid read) as extra cost on
>>> hdmi_check_hpd_state(), which kills half the purpose of this patch.
>>>
>> 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.
>
> For this to work like you want we need a bigger restructuring of HDMI
> and partly omapdss also. Currently we have just one big "enabled" or
> "disabled" state. We need multiple states. Probably something like:
>
> - disabled, everything totally off
> - low power, hotplug detection enabled
> - powered on, but no video
> - video enabled
>
> Been long in my mind, but I'm not very familiar with HDMI so I could get
> my simple prototypes to work when I tried something like this once.

That doesn't sound too hard since the difference between the first three 
states at the HDMI chip is just whether the two gpio controlling it are 
00, 10 or 11.

If Jassi's alright with it we might have a go at implementing this, but 
can you define a bit more about how we logically tell DSS that we want 
to, eg, disable HDMI totally?

-Andy

-- 
Andy Green | TI Landing Team Leader
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