On 27/11/2025 09:42, Luca Ceresoli wrote:
> 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@mgkdf6ztow42
> [1]
> https://lore.kernel.org/all/[email protected]/
> [2] https://lore.kernel.org/all/[email protected]/
>
> Closes:
> https://lore.kernel.org/r/bhkn6hley4xrol5o3ytn343h4unkwsr26p6s6ltcwexnrsjsdx@mgkdf6ztow42
> Cc: [email protected] # 6.15+
> Co-developed-by: Hervé Codina <[email protected]>
> Signed-off-by: Hervé Codina <[email protected]>
> Signed-off-by: Luca Ceresoli <[email protected]>
> ---
> Francesco, Emanuele, João: can you please apply this patch and report
> whether the display on the affected boards gets back to working as before?
>
> Cc: João Paulo Gonçalves <[email protected]>
> Cc: Francesco Dolcini <[email protected]>
> Cc: Emanuele Ghidoli <[email protected]>
> ---
> drivers/gpu/drm/bridge/ti-sn65dsi83.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> index 033c44326552..fffb47b62f43 100644
> --- 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(struct sn65dsi83
> *ctx)
> */
>
> 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(struct drm_bridge
> *bridge,
> 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);
>
> ---
> base-commit: c884ee70b15a8d63184d7c1e02eba99676a6fcf7
> change-id: 20251126-drm-ti-sn65dsi83-ignore-pll-unlock-4a28aa29eb5c
>
> Best regards,
Hi Luca,
the display works correctly with this patch, thanks!
Kind regards.
Tested-by: Emanuele Ghidoli <[email protected]>
