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
