Re: [PATCH 0/2] drm/tegra: Fix panel support on Venice 2 and Nyan

[Dmitry Osipenko <digetx@gmail.com>]

21.12.2021 21:01, Thierry Reding пишет:
> On Tue, Dec 21, 2021 at 07:45:31PM +0300, Dmitry Osipenko wrote:
>> 21.12.2021 19:17, Thierry Reding пишет:
>>> On Tue, Dec 21, 2021 at 06:47:31PM +0300, Dmitry Osipenko wrote:
>>>> 21.12.2021 13:58, Thierry Reding пишет:
>>>> ..
>>>>>>>> The panel->ddc isn't used by the new panel-edp driver unless panel is
>>>>>>>> compatible with "edp-panel". Hence the generic_edp_panel_probe() should
>>>>>>>> either fail or crash for a such "edp-panel" since panel->ddc isn't fully
>>>>>>>> instantiated, AFAICS.
>>>>>>>
>>>>>>> I've tested this and it works fine on Venice 2. Since that was the
>>>>>>> reference design for Nyan, I suspect that Nyan's will also work.
>>>>>>>
>>>>>>> It'd be great if Thomas or anyone else with access to a Nyan could
>>>>>>> test this to verify that.
>>>>>>
>>>>>> There is no panel-edp driver in the v5.15. The EOL of v5.15 is Oct,
>>>>>> 2023, hence we need to either use:
>>>>>
>>>>> All the (at least relevant) functionality that is in panel-edp was in
>>>>> panel-simple before it was moved to panel-edp. I've backported this set
>>>>> of patches to v5.15 and it works just fine there.
>>>>
>>>> Will we be able to add patch to bypass the panel's DT ddc-i2c-bus on
>>>> Nyan to keep the older DTBs working?
>>>
>>> I don't see why we would want to do that. It's quite clear that the DTB
>>> is buggy in this case and we have a more accurate way to describe what's
>>> really there in hardware. In addition that more accurate representation
>>> also gets rid of a bug. Obviously because the bug is caused by the
>>> previous representation that was not accurate.
>>>
>>> Given that we can easily replace the DTBs on these devices there's no
>>> reason to make this any more complicated than it has to be.
>>
>> Don't you care about normal people at all? Do you assume that everyone
>> must to be a kernel developer to be able to use Tegra devices? :/
> 
> If you know how to install a custom kernel you also know how to replace
> the DTB on these devices.
> 
> For everyone else, once these patches are merged upstream and
> distributions start shipping the new version, they will get this
> automatically by updating their kernel package since most distributions
> actually ship the DTB files as part of that.
> 
>> It's not a problem for you to figure out why display is broken, for
>> other people it's a problem. Usually nobody will update DTB without a
>> well known reason, instead device will be dusted on a shelf. In the end
>> you won't have any users at all.
> 
> Most "normal" people aren't even going to notice that their DTB is going
> to be updated. They would actually have to do extra work *not* to update
> it.

My past experience tells that your assumption is incorrect. There are
quite a lot of people who will update kernel, but not DTB.

ARM devices have endless variations of bootloaders and individual quirks
required for a successful installation of a kernel. Kernel update by
distro usually isn't a thing on ARM.