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Historically the expectation was to set brightness to max on enable, if it was zero. However, the policy should be to preserve brightness across disable/enable, for example the userspace might want to dim the brightness before disable (e.g. on suspend) and gradually bring it back up after enable (e.g. on resume). If the brightness gets bumped to max at enable, this causes flicker as the userspace expects the brightness to have been preserved across disable/enable. For example: (suspend) [53949.248875] i915 0000:00:02.0: [drm:intel_edp_backlight_off] [53949.452046] i915 0000:00:02.0: [drm:intel_backlight_set_pwm_level] set backlight PWM = 0 (wakeup) [53986.067356] i915 0000:00:02.0: [drm:intel_edp_backlight_on] [53986.067367] i915 0000:00:02.0: [drm:intel_backlight_enable] pipe A [53986.067476] i915 0000:00:02.0: [drm:intel_backlight_set_pwm_level] set backlight PWM = 96000 [53986.119766] backlight intel_backlight: PM: calling backlight_resume+0x0/0x7a @ 4916, parent: card0-eDP-1 [53986.119781] backlight intel_backlight: PM: backlight_resume+0x0/0x7a returned 0 after 0 usecs [53986.220068] [drm:intel_backlight_device_update_status] updating intel_backlight, brightness=26321/96000 [53986.220086] i915 0000:00:02.0: [drm:intel_panel_actually_set_backlight] set backlight level = 27961 Reduce the check to respecting the minimum brightness, and avoid bumping min brightness to max on enable. Note: It's possible there's still userspace out there that relies on the old behaviour. It would be unfortunate, but there's really only one way to find out. Cc: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com> Cc: Matt Roper <matthew.d.roper@intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Gareth Yu <gareth.yu@intel.com> Reviewed-by: Jani Nikula <jani.nikula@intel.com> [Jani: Rewrote the commit message.] Signed-off-by: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20240321045311.2124111-1-gareth.yu@intel.com |
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
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| samples | ||
| scripts | ||
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| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
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| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
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| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.