Re: drm: mipi_dbi_hw_reset() keeps display in reset

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On 15.03.2025 00:50, Alex Lanzano wrote:
> On Fri, Mar 14, 2025 at 12:57:27PM +0100, Josef Luštický wrote:
>> On Mon, Mar 10, 2025 at 7:33 PM Alex Lanzano <lanzano.alex@xxxxxxxxx> wrote:
>>>
>>> On Fri, Mar 07, 2025 at 10:25:18AM +0100, Josef Luštický wrote:
>>>> Ok, I'll implement the change and post it for a review.
>>>> About the property naming, I tend to name it something like
>>>> "inverted-reset-gpio-fixed" to denote that it is assumed the code
>>>> using the "reset-gpios" property was fixed.
>>>> What are your thoughts?
>>>>
>>>
>>> You probably wnat something more concise and in present tense like
>>> 'invert-reset-gpio'
>>
>> OK, I understand.
>> It still feels like the 'invert' would mean that the code is supposed
>> to do something non-standard with the reset-gpios property
>> specification.
>> How about 'correct-reset-gpio' or 'proper-reset-gpio' to denote that
>> the reset-gpio property describes the HW correctly.
>>
> 
> My main concern here is that the device tree properties are supposed to
> be completely independent of the driver code. So, I'd be hesitant to
> imply that a property 'fixes' a specific behavior in the driver in the
> name of the property itself (even though it does).
> 

I suggest you ask on the devicetree ML, they probably know how to handle
bugs like this.

Noralf.

> Best regards,
> Alex
> 
>>>> On Tue, Feb 25, 2025 at 2:46 PM Alex Lanzano <lanzano.alex@xxxxxxxxx> wrote:
>>>>>
>>>>> On Tue, Feb 25, 2025 at 12:59:59PM +0100, Josef Luštický wrote:
>>>>>> On Mon, Feb 24, 2025 at 12:13 AM Alex Lanzano <lanzano.alex@xxxxxxxxx> wrote:
>>>>>>>
>>>>>>> On Mon, Feb 17, 2025 at 12:39:01PM +0100, Josef Luštický wrote:
>>>>>>>> On Sat, Feb 15, 2025 at 8:14 PM Alex Lanzano <lanzano.alex@xxxxxxxxx> wrote:
>>>>>>>>>
>>>>>>>>> On Fri, Feb 14, 2025 at 08:04:41PM -0500, Alex Lanzano wrote:
>>>>>>>>>> On Fri, Feb 14, 2025 at 10:29:29AM +0100, Josef Luštický wrote:
>>>>>>>>>>> Hello Alex,
>>>>>>>>>>> there is a bug in mipi_dbi_hw_reset() function that implements the logic of
>>>>>>>>>>> display reset contrary.
>>>>>>>>>>> It keeps the reset line activated which keeps displays in reset state.
>>>>>>>>>>>
>>>>>>>>>>> I reported the bug to
>>>>>>>>>>> https://gitlab.freedesktop.org/drm/misc/kernel/-/issues/63
>>>>>>>>>>>
>>>>>>>>>>> Unfortunately, fixing the bug would mean current DTB-ABI breakage and
>>>>>>>>>>> device-trees modification would be needed.
>>>>>>>>>>> I mainly write this email to let you and other people know about it, so
>>>>>>>>>>> hopefully it can be found easier.
>>>>>>>>>>> What are your thoughts?
>>>>>>>>>> Thanks for making me aware. I'll dig into over the weekend and get back
>>>>>>>>>> to you
>>>>>>>>>
>>>>>>>>> Alright so I looked into a bit more. Looks like the MIPI Specification
>>>>>>>>> says that the reset line is active low. So, if we want dt entries to be
>>>>>>>>> correct the logic for setting the reset line in mipi_dbi_hw_reset()
>>>>>>>>> should be flipped. However, like you said, this is going to cause a some
>>>>>>>>> confused developers to break out their oscilloscopes to figure out
>>>>>>>>> why their display isn't working.
>>>>>>>>>
>>>>>>>>> Best regards,
>>>>>>>>> Alex
>>>>>>>>
>>>>>>>> Thank you Alex for looking into this.
>>>>>>>> I think all the supported dts can be changed together with
>>>>>>>> mipi_dbi_hw_reset(), however the fix would break existing DTBs and
>>>>>>>> third party DTSs.
>>>>>>>> So I think it shall be either noted somewhere that due to this bug,
>>>>>>>> the reset line needs to be "wrongly" ACTIVE_HIGH in DTS
>>>>>>>> or the mipi_dbi_hw_reset() is changed and the compatibility is broken,
>>>>>>>> which needs to be announced.
>>>>>>>>
>>>>>>>> BTW Zephyr fixed the code [1], but they introduced the MIPI DBI
>>>>>>>> support just a couple of weeks before the fix, so they avoided the
>>>>>>>> compatibility issue.
>>>>>>>> I was not able to find users mentioning issues related to the display
>>>>>>>> not functioning properly, so I had to dig into the code.
>>>>>>>> But afterwards I found a thread on Raspberry PI forums, where one of
>>>>>>>> the moderators mentions it [2].
>>>>>>>>
>>>>>>>> [1] https://github.com/zephyrproject-rtos/zephyr/issues/68562
>>>>>>>> [2] https://forums.raspberrypi.com/viewtopic.php?p=2165720#p2165720
>>>>>>>
>>>>>>> So, here are my thoughts on this after pondering it over for a bit.
>>>>>>> Ideally we should eventually reverse the reset logic so the DTS entry
>>>>>>> correctly specifies the hardware. However, instead of an abrupt change
>>>>>>> maybe we add an additional property to the DTS node that when present
>>>>>>> uses the correct reset logic. If the property isn't present we use the
>>>>>>> current incorrect reset logic and print out a dev_warn that it will soon
>>>>>>> be deprecated.
>>>>>>>
>>>>>>> Let me know what you think.
>>>>>>>
>>>>>>> Best regards,
>>>>>>> Alex
>>>>>>>
>>>>>>>
>>>>>> I think it's a good idea if the current logic is about to be fixed.
>>>>>> Another (probably not as good) idea is to introduce a new property
>>>>>> named "nreset-gpios = ..." or something like that, but I realise that
>>>>>> "reset-gpios" is the de-facto standard naming.
>>>>>>
>>>>>> Best regards,
>>>>>> Josef
>>>>>>
>>>>>
>>>>> Yeah I think it may be simpler to just add a boolean property like
>>>>> 'reverse-reset'. It would make the driver code simpler to implement too.
>>>>> Would you like to implement this change and submit the patch or would
>>>>> you like me to?
>>>>>
>>>>> Best regards,
>>>>> Alex




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