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Schwab" To: Hans de Goede Cc: Kate Hsuan , Jiri Kosina , Benjamin Tissoires , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] HID: lg-g15 - Add support for Logitech G13. Message-ID: References: <8ae2cc92-5dfe-466d-95fd-da74309d7244@kernel.org> <2de88077-eb8d-44ad-a96a-5db889913cba@kernel.org> <64b1c076-f1f7-45a3-900a-dd52ab50cd4e@kernel.org> <8e2c3560-6cba-4808-8207-ba3e1dd0e661@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8e2c3560-6cba-4808-8207-ba3e1dd0e661@kernel.org> On Wed, Sep 17, 2025 at 12:33:36PM +0200, Hans de Goede wrote: > On 16-Sep-25 00:18, Leo L. Schwab wrote: > > What do you want to happen to `brightness_hw_changed` when > > `brightness` is changed in sysfs while the backlight is on? As it stands, > > the current behavior is: > > * Driver loads and probes; `brightness` and `brightness_hw_changed` > > both set to 255. > > Ack, except that as mentioned above I would not touch brightness_hw_changed > and just leave it at -1. > > > * sysfs `brightness` changed to 128. `brightness_hw_changed` > > remains at 255. > > * Toggle backilght off. `brightness_hw_changed` changed to 0. > > `brightness` remains at 128. > > * Toggle backlight back on. `brightness_hw_changed` gets a copy of > > `brightness`, and both are now 128. > > Ack this is all correct. > ...Oy. Okay, I can give you that. > > This seems inconsistent to me. > > This is working as intended / how the API was designed as > Documentation/ABI/testing/sysfs-class-led says: > > Reading this file will return the last brightness level set > by the hardware, this may be different from the current > brightness. Reading this file when no hw brightness change > event has happened will return an ENODATA error. > First: Why isn't this mentioned in Documentation/leds/leds_class.rst? And second: This doesn't really clarify anything. That paragraph may be legitimately interpreted to mean that `brightness_hw_changed` is completely independent of `brightness`, as it was in my original implementation. > > Hence my earlier suggestion that > > `brightness_hw_changed` should track all changes to `brightness`, except > > when the backlight is toggled off. > > Then it also would be reporting values coming from sysfs writes, > which it explicitly should not do. > Okay, fair, but having `brightness_hw_changed` read as 255, then later as 128 after hitting the toggle button a couple of times strikes me as inconsistent behavior. > Summarizing in my view the following changes are necessary on v4: > > 1. Add backlight_disabled (or backlight_enabled) flag to struct lg_g15_data > 2. Init that flag from prope() > 3. Use that flag on receiving input reports to see if notify() > should be called > 4. Replace the LED_FULL passed to notify() (for off->on) > with g15_led->brightness > Will do; will post v6 shortly. And someone should update the docs describing the expected interaction between `brightness` and `brightness_hw_changed`. Schwab