Messages in this thread | | | From | Joonas Kylmälä <> | Subject | Re: [PATCH] drm/panel: samsung: s6e8aa0: Add backlight control support | Date | Mon, 23 Sep 2019 20:57:17 +0300 |
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Hi,
thanks a lot for the review, Andrzej!
Andrzej Hajda: >> +static const struct backlight_ops s6e8aa0_backlight_ops = { >> + .update_status = s6e8aa0_set_brightness, > > > This is racy, update_status can be called in any time between probe and > remove, particularly: > > a) before panel enable, > > b) during panel enable, > > c) when panel is enabled, > > d) during panel disable, > > e) after panel disable, > > > b and d are racy for sure - backlight and drm callbacks are async. > > IMO the best solution would be to register backlight after attaching > panel to drm, but for this drm_panel_funcs should have attach/detach > callbacks (like drm_bridge_funcs), > > then update_status callback should take some drm_connector lock to > synchronize with drm, and write to hw only when pipe is enabled.
I will start reading the kernel DRM KMS documentation in order to learn how the attach callback would fit in the picture and do what you suggest but it might take a few weeks or months.
Also, as a lot of this code was mimicked from drivers/gpu/drm/panel/panel-samsung-s6e63m0.c it looks like that is also having this race condition. Unfortunately, I don't think I have the s6e63m0 panel so for that I probably cannot fix this issue.
Joonas
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