Il 27/01/22 16:46, AngeloGioacchino Del Regno ha scritto:
Il 27/01/22 16:21, Chun-Kuang Hu ha scritto:
Hi, Angelo:
AngeloGioacchino Del Regno angelogioacchino.delregno@collabora.com 於 2022年1月27日 週四 下午10:36寫道：
DRM bridge drivers are now attaching their DSI device at probe time, which requires us to register our DSI host in order to let the bridge to probe: this recently started producing an endless -EPROBE_DEFER loop on some machines that are using external bridges, like the parade-ps8640, found on the ACER Chromebook R13.
Now that the DSI hosts/devices probe sequence is documented, we can do adjustments to the mtk_dsi driver as to both fix now and make sure to avoid this situation in the future: for this, following what is documented in drm_bridge.c, move the mtk_dsi component_add() to the mtk_dsi_ops.attach callback and delete it in the detach callback; keeping in mind that we are registering a drm_bridge for our DSI, which is only used/attached if the DSI Host is bound, it wouldn't make sense to keep adding our bridge at probe time (as it would be useless to have it if mtk_dsi_ops.attach() fails!), so also move that one to the dsi host attach function (and remove it in detach).
Fixes: 209264a85707 ("drm/bridge: Document the probe issue with MIPI-DSI bridges")
The fixed tag should indicate the patch which cause the bug, but why a patch just adding document would cause bug? So no any patch cause bug? This patch just want to prevent a possible bug?
I think you've missed my previous message on v2, so I will paste it here:
unfortunately I couldn't find a valid commit for a Fixes tag. This started being an issue at some point, when the DRM was changed to adhere to the documented probe sequence: the MediaTek DSI driver was not the only one that got broken/affected by these changes.
If you have any advice on which commit should be tagged, I'm open for any kind of suggestion.
I tried to check on other drivers which got fixed for the same behavior, for example drm/msm, but none of them had a Fixes tag. When the DRM got changed to adhere to this sequence, some drm/bridge drivers were also changed; this has created some incompatibilities with some drm drivers, including drm/msm and drm/mediatek.
This commit is not fixing a latent bug that was introduced in drm/mediatek but rather one that was induced by the new, fixed, probe flow that got recently documented - and to which drivers should adhere; failing to adhere to that will produce an endless -EPROBE_DEFER loop, due to other drivers (as mentioned, for example drm/bridge drivers) having been changed to use that probe sequence.
Regards, Angelo
I've been thinking about another solution to this issue.
Would it be fine if I send a v4 that removes the Fixes tag, but adds the following?
Cc: stable@kernel.org # v5.15+
Regards, Chun-Kuang.
Signed-off-by: AngeloGioacchino Del Regno angelogioacchino.delregno@collabora.com Reviewed-by: Andrzej Hajda andrzej.hajda@intel.com Reviewed-by: Jagan Teki jagan@amarulasolutions.com
drivers/gpu/drm/mediatek/mtk_dsi.c | 167 +++++++++++++++-------------- 1 file changed, 84 insertions(+), 83 deletions(-)