On Thu, 14 Jan 2021, Jani Nikula <jani.nikula@xxxxxxxxx> wrote: > On Wed, 13 Jan 2021, Lyude Paul <lyude@xxxxxxxxxx> wrote: >> Currently, every different type of backlight hook that i915 supports is >> pretty straight forward - you have a backlight, probably through PWM >> (but maybe DPCD), with a single set of platform-specific hooks that are >> used for controlling it. >> >> HDR backlights, in particular VESA and Intel's HDR backlight >> implementations, can end up being more complicated. With Intel's >> proprietary interface, HDR backlight controls always run through the >> DPCD. When the backlight is in SDR backlight mode however, the driver >> may need to bypass the TCON and control the backlight directly through >> PWM. >> >> So, in order to support this we'll need to split our backlight callbacks >> into two groups: a set of high-level backlight control callbacks in >> intel_panel, and an additional set of pwm-specific backlight control >> callbacks. This also implies a functional changes for how these >> callbacks are used: >> >> * We now keep track of two separate backlight level ranges, one for the >> high-level backlight, and one for the pwm backlight range >> * We also keep track of backlight enablement and PWM backlight >> enablement separately >> * Since the currently set backlight level might not be the same as the >> currently programmed PWM backlight level, we stop setting >> panel->backlight.level with the currently programmed PWM backlight >> level in panel->backlight.pwm_funcs->setup(). Instead, we rely >> on the higher level backlight control functions to retrieve the >> current PWM backlight level (in this case, intel_pwm_get_backlight()). >> Note that there are still a few PWM backlight setup callbacks that >> do actually need to retrieve the current PWM backlight level, although >> we no longer save this value in panel->backlight.level like before. >> >> Additionally, we drop the call to lpt_get_backlight() in >> lpt_setup_backlight(), and avoid unconditionally writing the PWM value that >> we get from it and only write it back if we're in CPU mode, and switching >> to PCH mode. The reason for this is because in the original codepath for >> this, it was expected that the intel_panel_bl_funcs->setup() hook would be >> responsible for fetching the initial backlight level. On lpt systems, the >> only time we could ever be in PCH backlight mode is during the initial >> driver load - meaning that outside of the setup() hook, lpt_get_backlight() >> will always be the callback used for retrieving the current backlight >> level. After this patch we still need to fetch and write-back the PCH >> backlight value if we're switching from CPU mode to PCH, but because >> intel_pwm_setup_backlight() will retrieve the backlight level after setup() >> using the get() hook, which always ends up being lpt_get_backlight(). Thus >> - an additional call to lpt_get_backlight() in lpt_setup_backlight() is >> made redundant. >> >> v7: >> * Use panel->backlight.pwm_funcs->get() to get the backlight level in >> intel_pwm_setup_backlight(), lest we upset lockdep > > I think this change is wrong, as it now bypasses > intel_panel_invert_pwm_level(). Please explain. I don't see anything in > there that could trigger a lockdep warning. > > Perhaps it's the below you're referring to, but I think the root cause > is different? > >> @@ -1788,22 +1780,17 @@ static int vlv_setup_backlight(struct intel_connector *connector, enum pipe pipe >> panel->backlight.active_low_pwm = ctl2 & BLM_POLARITY_I965; >> >> ctl = intel_de_read(dev_priv, VLV_BLC_PWM_CTL(pipe)); >> - panel->backlight.max = ctl >> 16; >> + panel->backlight.pwm_level_max = ctl >> 16; >> >> - if (!panel->backlight.max) >> - panel->backlight.max = get_backlight_max_vbt(connector); >> + if (!panel->backlight.pwm_level_max) >> + panel->backlight.pwm_level_max = get_backlight_max_vbt(connector); >> >> - if (!panel->backlight.max) >> + if (!panel->backlight.pwm_level_max) >> return -ENODEV; >> >> - panel->backlight.min = get_backlight_min_vbt(connector); >> + panel->backlight.pwm_level_min = get_backlight_min_vbt(connector); >> >> - val = _vlv_get_backlight(dev_priv, pipe); > > Turns out this is a meaningful change, as the higher level > vlv_get_backlight() function that will be called instead hits: > > <4>[ 12.870202] i915 0000:00:02.0: drm_WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex)) > > in intel_connector_get_pipe(connector). > > It's a real problem. See this, it's obvious (in retrospect): > > https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_19348/fi-bsw-kefka/igt@runner@xxxxxxxxxxxx > https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_19348/fi-bsw-kefka/boot0.txt > > I don't have a quick answer how this could be handled neatly. Perhaps > the ->get call (or rather, intel_pwm_get_backlight) to set > panel->backlight.level needs to be spread out to the end of each > pwm_funcs->setup function after all? Though it's at the wrong > abstraction level wrt level being a higher level, uh, level. > > I don't think it's enough to just grab connection_mutex around setup > (and even checking if we can do that is a bunch of digging) - I think > it's likely intel_connector_get_pipe() returns INVALID_PIPE at that > point. > > Okay, here's a clumsy suggestion that I think works around this and > unblocks the series until we figure out a better way: > > 1. At the end of vlv_setup_backlight(): > > /* add fixme comment about how wrong this is */ > panel->backlight.level = intel_panel_invert_pwm_level(connector, _vlv_get_backlight()); > > > 2. In intel_pwm_setup_backlight() only set level if ->setup didn't: > > if (!panel->backlight.level) > panel->backlight.level = intel_pwm_get_backlight(connector); Of course, if ->setup ends up setting the level to 0, it hits the same issue. :( > > What do you think? > > BR, > Jani. > >> - val = intel_panel_compute_brightness(connector, val); >> - panel->backlight.level = clamp(val, panel->backlight.min, >> - panel->backlight.max); >> - >> - panel->backlight.enabled = ctl2 & BLM_PWM_ENABLE; >> + panel->backlight.pwm_enabled = ctl2 & BLM_PWM_ENABLE; >> >> return 0; >> } >> @@ -1828,24 +1815,18 @@ bxt_setup_backlight(struct intel_connector *connector, enum pipe unused) -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
