On Sat, Feb 15, 2025 at 8:14 PM Alex Lanzano <lanzano.a...@gmail.com> 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 Best regards, Josef
