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[82.37.195.13]) by smtp.gmail.com with ESMTPSA id f10-20020a7bcd0a000000b003fa99969e61sm24767384wmj.45.2023.07.04.08.40.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Jul 2023 08:40:52 -0700 (PDT) Date: Tue, 4 Jul 2023 16:40:51 +0100 From: Daniel Thompson To: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= Cc: Lee Jones , Jingoo Han , Helge Deller , dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] backlight: led_bl: fix initial power state Message-ID: <20230704154051.GC385243@aspen.lan> References: <20230704140750.25799-1-mans@mansr.com> <20230704150310.GA385243@aspen.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 04, 2023 at 04:31:51PM +0100, Måns Rullgård wrote: > Daniel Thompson writes: > > > On Tue, Jul 04, 2023 at 03:07:50PM +0100, Mans Rullgard wrote: > >> The condition for the initial power state based on the default > >> brightness value is reversed. Fix it. > >> > >> Fixes: ae232e45acf9 ("backlight: add led-backlight driver") > >> Signed-off-by: Mans Rullgard > >> --- > >> drivers/video/backlight/led_bl.c | 4 ++-- > >> 1 file changed, 2 insertions(+), 2 deletions(-) > >> > >> diff --git a/drivers/video/backlight/led_bl.c b/drivers/video/backlight/led_bl.c > >> index 3259292fda76..28e83618a296 100644 > >> --- a/drivers/video/backlight/led_bl.c > >> +++ b/drivers/video/backlight/led_bl.c > >> @@ -200,8 +200,8 @@ static int led_bl_probe(struct platform_device *pdev) > >> props.type = BACKLIGHT_RAW; > >> props.max_brightness = priv->max_brightness; > >> props.brightness = priv->default_brightness; > >> - props.power = (priv->default_brightness > 0) ? FB_BLANK_POWERDOWN : > >> - FB_BLANK_UNBLANK; > >> + props.power = (priv->default_brightness > 0) ? FB_BLANK_UNBLANK : > >> + FB_BLANK_POWERDOWN; > > > > The logic was wrong before but I think will still be wrong after the > > change too (e.g. the bogus logic is probably avoiding backlight flicker > > in some use cases). > > > > The logic here needs to be similar to what pwm_bl.c implements in > > pwm_backlight_initial_power_state(). Whilst it might be better > > to implement this in led_bl_get_leds() let me show what I mean > > in code that fits in the current line: > > > > /* > > * Activate the backlight if the LEDs are already lit *or* > > * there is no phandle link (meaning the backlight power > > * state cannot be synced with the display state). > > */ > > props.power = (active_at_boot || !dev->node->phandle) ? > > FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN; > > > > Note that active_at_boot is not the same as (priv->default_brightness > 0) > > since the value read by led_bl_get_leds() can be clobbered when we > > parse the properties. > > Am I understanding correctly that the code should be using the > default_brightness value as set by led_bl_get_leds() to determine the > initial power state, not whatever default value the devicetree provides? Yes. The devicetree allows us to specify a default brightness but the DT value cannot not be used to decide if the backlight has already been lit up. Daniel.