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); 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
