6.18-stable review patch. If anyone has any objections, please let me know.
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From: Luca Ceresoli luca.ceresoli@bootlin.com
commit 35e282c1868de3c9d15f9a8812cbb2e7da06b0c1 upstream.
On hardware based on Toradex Verdin AM62 the recovery mechanism added by commit ad5c6ecef27e ("drm: bridge: ti-sn65dsi83: Add error recovery mechanism") has been reported [0] to make the display turn on and off and and the kernel logging "Unexpected link status 0x01".
According to the report, the error recovery mechanism is triggered by the PLL_UNLOCK error going active. Analysis suggested the board is unable to provide the correct DSI clock neede by the SN65DSI84, to which the TI SN65DSI84 reacts by raising the PLL_UNLOCK, while the display still works apparently without issues.
On other hardware, where all the clocks are within the components specifications, the PLL_UNLOCK bit does not trigger while the display is in normal use. It can trigger for e.g. electromagnetic interference, which is a transient event and exactly the reason why the error recovery mechanism has been implemented.
Idelly the PLL_UNLOCK bit could be ignored when working out of specification, but this requires to detect in software whether it triggers because the device is working out of specification but visually correctly for the user or for good reasons (e.g. EMI, or even because working out of specifications but compromising the visual output).
The ongoing analysis as of this writing [1][2] has not yet found a way for the driver to discriminate among the two cases. So as a temporary measure mask the PLL_UNLOCK error bit unconditionally.
[0] https://lore.kernel.org/r/bhkn6hley4xrol5o3ytn343h4unkwsr26p6s6ltcwexnrsjsdx... [1] https://lore.kernel.org/all/b71e941c-fc8a-4ac1-9407-0fe7df73b412@gmail.com/ [2] https://lore.kernel.org/all/20251125103900.31750-1-francesco@dolcini.it/
Fixes: ad5c6ecef27e ("drm: bridge: ti-sn65dsi83: Add error recovery mechanism") Closes: https://lore.kernel.org/r/bhkn6hley4xrol5o3ytn343h4unkwsr26p6s6ltcwexnrsjsdx... Cc: stable@vger.kernel.org # 6.15+ Reported-by: João Paulo Gonçalves joao.goncalves@toradex.com Tested-by: Emanuele Ghidoli emanuele.ghidoli@toradex.com Co-developed-by: Hervé Codina herve.codina@bootlin.com Signed-off-by: Hervé Codina herve.codina@bootlin.com Signed-off-by: Luca Ceresoli luca.ceresoli@bootlin.com Link: https://patch.msgid.link/20251127-drm-ti-sn65dsi83-ignore-pll-unlock-v1-1-8a... Signed-off-by: Maxime Ripard mripard@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/bridge/ti-sn65dsi83.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
--- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c @@ -429,7 +429,14 @@ static void sn65dsi83_handle_errors(stru */
ret = regmap_read(ctx->regmap, REG_IRQ_STAT, &irq_stat); - if (ret || irq_stat) { + + /* + * Some hardware (Toradex Verdin AM62) is known to report the + * PLL_UNLOCK error interrupt while working without visible + * problems. In lack of a reliable way to discriminate such cases + * from user-visible PLL_UNLOCK cases, ignore that bit entirely. + */ + if (ret || irq_stat & ~REG_IRQ_STAT_CHA_PLL_UNLOCK) { /* * IRQ acknowledged is not always possible (the bridge can be in * a state where it doesn't answer anymore). To prevent an @@ -654,7 +661,7 @@ static void sn65dsi83_atomic_enable(stru if (ctx->irq) { /* Enable irq to detect errors */ regmap_write(ctx->regmap, REG_IRQ_GLOBAL, REG_IRQ_GLOBAL_IRQ_EN); - regmap_write(ctx->regmap, REG_IRQ_EN, 0xff); + regmap_write(ctx->regmap, REG_IRQ_EN, 0xff & ~REG_IRQ_EN_CHA_PLL_UNLOCK_EN); } else { /* Use the polling task */ sn65dsi83_monitor_start(ctx);