Re: [PATCH] tegra: ventana: display and backlight DT entries

[Mark Zhang <markz-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On 11/14/2012 01:56 PM, Mark Zhang wrote:
> On 11/14/2012 01:36 PM, Alex Courbot wrote:
>> On Wednesday 14 November 2012 00:46:52 Stephen Warren wrote:
>>> I do tend to think that we should use EDID where there is one.
>>>
>>> 1) If there is an EDID in the panel HW, and the panel's I2C is hooked
>>> up to Tegra, we should read it out at runtime.
>>
>> According to Ventana' platform design guide the LCD panel is hooked on I2C2. 
>> The panel's data sheet lists CLK_EDID and DATA_EDID pins, which I assume are 
>> for I2C, but there is no mention of an I2C address in both guides.
>>
> 
> Normally the address is 0x50. Take a look at function
> "drm_do_probe_ddc_edid" as a reference.
> 
>>> 2) Otherwise, if the panel's documentation provides an EDID, we should
>>> use that, since it's the most canonical/common/standard representation
>>> of the panel's properties.
>>
>> Panel's documentation indeed provides full EDID specification in appendix. Mark 
>> sent me an EDID blob which works but I don't know where it comes from - Mark, 
>> could you tell us?
>>
> 
> Actually I use a tool named "i2cget" to get this 128 bytes EDID. For
> Ventana, I use a script like this:
> 
> for i in  $(seq 0 127)
> do
> 	#echo " Reading byte no : $i "
> 	i2cget -y 0 0x50 $i | xxd -r -p >> tegra20-ventana.edid

Sorry, this should be: i2cget -y 2 0x50 $i...

> done
> 
>>> 3) Otherwise, use the videomode DT bindings.
>>>
>>> Another benefit of (2) is that we can actually support the panel
>>> without waiting for the videomode DT bindings to be finalized and merged.
>>
>> Is there another incentive for preferring (2) over (3)? EDID specs can easily 
>> be turned into videomode bindings, and it would also avoid introducing a new 
>> file into the kernel source.
>>
>>> Although if Ventana requires the power sequences helpers, that already
>>> means we won't be able to support Ventana's panel in 3.8 unless the
>>> power sequences code gets merged for 3.8; is that likely?
>>
>> Likely, I don't know, possible - maybe. Power seqs work and I could push to 
>> get them merged, but the following points need to be considered:
>> - DT bindings are likely to change from their current form. I want to take 
>> advantage of the gpio API changes that are undergoing, and also probably of 
>> your preprocessor patch for dtc (not sure if that is already usable in the 
>> kernel?). Considering the feature is young I don't think a DT change would be 
>> a big deal, but the general consensus seems to be that DT bindings are 
>> immutable - maybe my perception is wrong?
>> - If I am to take maintainership of the feature, I guess I will have to get 
>> the patches sufficiently Ack'ed by enough people, and also have someone else 
>> pull from my tree (Linus? Or maybe some other power maintainer?). I am not 
>> familiar with the exact procedure here - moreover, my GPG key only has one 
>> signature from a trusted kernel dev, I am not sure if this is enough.
>>
>> Alex.
>>
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