Hi Maxime, On Mon, 1 Dec 2025 17:36:13 +0100 Maxime Ripard <[email protected]> wrote:
> Hi, > > On Thu, Nov 27, 2025 at 09:46:07AM +0100, Luca Ceresoli wrote: > > Hello Francesco, all, > > > > On Tue Nov 25, 2025 at 11:38 AM CET, Francesco Dolcini wrote: > > > From: Francesco Dolcini <[email protected]> > > > > > > This reverts commit ad5c6ecef27e ("drm: bridge: ti-sn65dsi83: Add error > > > recovery mechanism"). > > > > > > The reverted commit introduces a regression on Verdin AM62, and > > > potentially on more devices, not being able to generate a clock > > > that the TI SN65DSI83 PLL can lock to, with the display periodically > > > blinking. > > > > > > Verdin AM62 SoM has a Toshiba TC358778 DPI to DSI bridge, that can be > > > connected to an LVDS display over a TI SN65DSI83 bridge. Before this > > > change despite the TI SN65DSI83 reporting with a debug print a PLL > > > locking error the display was working fine with no visible glitches. > > > > > > The reasons for this issue was investigated without getting to a final > > > conclusion: > > > > > > - the DPI clock was measure and it is stable/accurate > > > - the DSI clock was not possible to measure, but this setup is used > > > with other display/bridges with no known issues > > > - the DSI clock is configured in continuous mode > > > - the actual DSI clock generated from the TC358778 is generate with a > > > PLL from a 25MHz reference clock > > > - it's not clear why some frequencies are working and some are not, for > > > example 50000000, 68750000, 72750000, 75000000 frequencies are fine, > > > while 69750000, 71100000, 72500000 are not > > > > > > Given that the safest approach is to just revert the commit, till a > > > proper solution for error recovery that is not introducing regression > > > is figured out. > > > > > > Reported-by: João Paulo Gonçalves <[email protected]> > > > Closes: > > > https://lore.kernel.org/all/bhkn6hley4xrol5o3ytn343h4unkwsr26p6s6ltcwexnrsjsdx@mgkdf6ztow42/ > > > Fixes: ad5c6ecef27e ("drm: bridge: ti-sn65dsi83: Add error recovery > > > mechanism") > > > Cc: [email protected] > > > Signed-off-by: Francesco Dolcini <[email protected]> > > > > Thanks for having sent this revert patch. > > > > However after evaluating the overall situation I decided to send a > > different patch to address this issue in the short term. The idea is to > > just ignore the PLL_UNLOCK error, keeping the existing > > structure. Rationale: > > > > * this sloves the issue for Toradex, based on João's initial report > > * there is no evidence of any bugs in the recovery mechanism, it's > > just exposing a pre-existing problem that was only producing a > > non-fatal dev_err() before > > * a full revert would remove error checking for all errors, including > > those not creating any issue, thus removing a useful feature > > * a full revert would require rewriting patches such as [0] (not a big > > deal per se, but see next bullet) > > * after patches such as [0] are applied, re-adding the error recovery > > mechanism would require another rework, so more work for authors, > > reviewers, testers and maintainers > > Were are we on this? Both patches work for me, but we need to take a decision. > IMHO, Luca's patch [0] is more interesting than this current patch doing a full revert. Indeed, Luca's patch keeps the monitoring active except for cases we known broken. Francesco, Emanuele, João have you had time to test Luca's patch ? [0] https://lore.kernel.org/all/20251127-drm-ti-sn65dsi83-ignore-pll-unlock-v1-1-8a03fdf56...@bootlin.com/ Best regards, Hervé
