Re: Bug in mipi_dbi_hw_reset() causes incorrect DT entries

[Krzysztof Kozlowski <krzk@kernel.org>]

On 15/03/2025 16:20, Alex Lanzano wrote:
> Hi all,
> 
> There is a bug in the mipi_dbi_hw_reset() function that handles the
> reset logic of the controller. Currently, it will set the reset gpio
> value to 0, wait a specified time, then set the reset gpio value to 1.
> 
> The issue with this implementation is that the MIPI DBI spec states that
> the reset signal is active low. So, in order to correct for this logic,
> the developer needs to incorrectly define the reset gpio as active high
> in the DT.

You should address it to driver and subsystem maintainers. Instead you
skipped all maintainers but Cc-ed people who have nothing to do with
MIPI DBI drivers in the kernel.

> 
> Fixing the logic in the driver would cause all the displays using this
> driver downstream to stop working. To mitigate this, Josef and I were
> thinking about adding an additional boolean property to the DT that when
> present would use the correct reset logic in the driver. And if it's not
> present use the current reset logic and print out a warning that this
> reset logic is deprecated.
> 
> The overall plan would be to have this temporary fix for a few release
> cycles so downstream has time to be aware of the issue and update their
> DT. Eventually, we would remove the incorrect reset logic in the driver
> and this addtional boolean property.

That's an ABI now, so you cannot change it without affecting users. Code
is from 2018 so you have plenty of users now.

I did some workaround for wsa88xx speakers but that's an exception and
it should not necessarily be a pattern to follow.

Not sure if it the issue is worth changing considering the impact.


Best regards,
Krzysztof