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Mon, 12 Jan 2026 23:17:03 -0800 (PST) Message-ID: <1fedb7d7-3a30-4f0f-961f-09613f2a95d0@gmail.com> Date: Tue, 13 Jan 2026 12:47:26 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] backlight: gpio: add support for multiple GPIOs for backlight control To: Daniel Thompson Cc: lee@kernel.org, danielt@kernel.org, jingoohan1@gmail.com, deller@gmx.de, pavel@kernel.org, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-leds@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260105085120.230862-1-tessolveupstream@gmail.com> <20260105085120.230862-3-tessolveupstream@gmail.com> Content-Language: en-US From: tessolveupstream@gmail.com In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 05-01-2026 15:39, Daniel Thompson wrote: > On Mon, Jan 05, 2026 at 02:21:20PM +0530, Sudarshan Shetty wrote: >> Extend the gpio-backlight driver to handle multiple GPIOs instead of a >> single one. This allows panels that require driving several enable pins >> to be controlled by the backlight framework. >> >> Signed-off-by: Sudarshan Shetty >> --- >> drivers/video/backlight/gpio_backlight.c | 61 +++++++++++++++++------- >> 1 file changed, 45 insertions(+), 16 deletions(-) >> >> diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c >> index 728a546904b0..037e1c111e48 100644 >> --- a/drivers/video/backlight/gpio_backlight.c >> +++ b/drivers/video/backlight/gpio_backlight.c >> @@ -17,14 +17,18 @@ >> >> struct gpio_backlight { >> struct device *dev; >> - struct gpio_desc *gpiod; >> + struct gpio_desc **gpiods; >> + unsigned int num_gpios; > > Why not use struct gpio_descs for this? > > Once you do that, then most of the gbl->num_gpios loops can be replaced with > calls to the array based accessors. > Based on your feedback, I have updated the implementation to use struct gpio_descs and array-based accessors, as recommended like below: git diff drivers/video/backlight/gpio_backlight.c diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c index 037e1c111e48..e99d7a9dc670 100644 --- a/drivers/video/backlight/gpio_backlight.c +++ b/drivers/video/backlight/gpio_backlight.c @@ -14,22 +14,37 @@ #include #include #include +#include struct gpio_backlight { struct device *dev; - struct gpio_desc **gpiods; + struct gpio_descs *gpiods; unsigned int num_gpios; }; static int gpio_backlight_update_status(struct backlight_device *bl) { struct gpio_backlight *gbl = bl_get_data(bl); - unsigned int i; + unsigned int n = gbl->num_gpios; int br = backlight_get_brightness(bl); + unsigned long *value_bitmap; + int words = BITS_TO_LONGS(n); + + value_bitmap = kcalloc(words, sizeof(unsigned long), GFP_KERNEL); + if (!value_bitmap) + return -ENOMEM; + + if (br) + bitmap_fill(value_bitmap, n); + else + bitmap_zero(value_bitmap, n); - for (i = 0; i < gbl->num_gpios; i++) - gpiod_set_value_cansleep(gbl->gpiods[i], br); + gpiod_set_array_value_cansleep(gbl->gpiods->ndescs, + gbl->gpiods->desc, + gbl->gpiods->info, + value_bitmap); + kfree(value_bitmap); return 0; } @@ -67,22 +82,18 @@ static int gpio_backlight_probe(struct platform_device *pdev) def_value = device_property_read_bool(dev, "default-on"); - gbl->num_gpios = gpiod_count(dev, NULL); + gbl->gpiods = devm_gpiod_get_array(dev, NULL, GPIOD_ASIS); + if (IS_ERR(gbl->gpiods)) { + if (PTR_ERR(gbl->gpiods) == -ENODEV) + return dev_err_probe(dev, -EINVAL, + "The gpios parameter is missing or invalid\n"); + return PTR_ERR(gbl->gpiods); + } + + gbl->num_gpios = gbl->gpiods->ndescs; if (gbl->num_gpios == 0) return dev_err_probe(dev, -EINVAL, "The gpios parameter is missing or invalid\n"); - gbl->gpiods = devm_kcalloc(dev, gbl->num_gpios, sizeof(*gbl->gpiods), - GFP_KERNEL); - if (!gbl->gpiods) - return -ENOMEM; - - for (i = 0; i < gbl->num_gpios; i++) { - gbl->gpiods[i] = - devm_gpiod_get_index(dev, NULL, i, GPIOD_ASIS); - if (IS_ERR(gbl->gpiods[i])) - return dev_err_probe(dev, PTR_ERR(gbl->gpiods[i]), - "Failed to get GPIO at index %u\n", i); - } memset(&props, 0, sizeof(props)); props.type = BACKLIGHT_RAW; @@ -101,14 +112,26 @@ static int gpio_backlight_probe(struct platform_device *pdev) : BACKLIGHT_POWER_OFF; } else { bool all_high = true; - - for (i = 0; i < gbl->num_gpios; i++) { - if (gpiod_get_value_cansleep(gbl->gpiods[i]) != 0) { - all_high = false; - break; - } + unsigned long *value_bitmap; + int words = BITS_TO_LONGS(gbl->num_gpios); + + value_bitmap = kcalloc(words, sizeof(unsigned long), GFP_KERNEL); + if (!value_bitmap) + return -ENOMEM; + + ret = gpiod_get_array_value_cansleep(gbl->gpiods->ndescs, + gbl->gpiods->desc, + gbl->gpiods->info, + value_bitmap); + if (ret) { + kfree(value_bitmap); + return dev_err_probe(dev, ret, + "failed to read initial gpio values\n"); } + all_high = bitmap_full(value_bitmap, gbl->num_gpios); + + kfree(value_bitmap); bl->props.power = all_high ? BACKLIGHT_POWER_ON : BACKLIGHT_POWER_OFF; } @@ -118,7 +141,7 @@ static int gpio_backlight_probe(struct platform_device *pdev) init_brightness = backlight_get_brightness(bl); for (i = 0; i < gbl->num_gpios; i++) { - ret = gpiod_direction_output(gbl->gpiods[i], init_brightness); + ret = gpiod_direction_output(gbl->gpiods->desc[i], init_brightness); if (ret) return dev_err_probe(dev, ret, "failed to set gpio %u direction\n", Could you please share your thoughts on whether this approach aligns with your expectations? > >> }; >> >> static int gpio_backlight_update_status(struct backlight_device *bl) >> { >> struct gpio_backlight *gbl = bl_get_data(bl); >> + unsigned int i; >> + int br = backlight_get_brightness(bl); >> >> - gpiod_set_value_cansleep(gbl->gpiod, backlight_get_brightness(bl)); >> + for (i = 0; i < gbl->num_gpios; i++) >> + gpiod_set_value_cansleep(gbl->gpiods[i], br); >> >> return 0; >> } >> @@ -52,6 +56,7 @@ static int gpio_backlight_probe(struct platform_device *pdev) >> struct backlight_device *bl; >> struct gpio_backlight *gbl; >> int ret, init_brightness, def_value; >> + unsigned int i; >> >> gbl = devm_kzalloc(dev, sizeof(*gbl), GFP_KERNEL); >> if (gbl == NULL) >> @@ -62,10 +67,22 @@ static int gpio_backlight_probe(struct platform_device *pdev) >> >> def_value = device_property_read_bool(dev, "default-on"); >> >> - gbl->gpiod = devm_gpiod_get(dev, NULL, GPIOD_ASIS); >> - if (IS_ERR(gbl->gpiod)) >> - return dev_err_probe(dev, PTR_ERR(gbl->gpiod), >> - "The gpios parameter is missing or invalid\n"); >> + gbl->num_gpios = gpiod_count(dev, NULL); >> + if (gbl->num_gpios == 0) >> + return dev_err_probe(dev, -EINVAL, >> + "The gpios parameter is missing or invalid\n"); >> + gbl->gpiods = devm_kcalloc(dev, gbl->num_gpios, sizeof(*gbl->gpiods), >> + GFP_KERNEL); >> + if (!gbl->gpiods) >> + return -ENOMEM; > > This is definitely easier if you simply use devm_get_array(). > > >> + >> + for (i = 0; i < gbl->num_gpios; i++) { >> + gbl->gpiods[i] = >> + devm_gpiod_get_index(dev, NULL, i, GPIOD_ASIS); >> + if (IS_ERR(gbl->gpiods[i])) >> + return dev_err_probe(dev, PTR_ERR(gbl->gpiods[i]), >> + "Failed to get GPIO at index %u\n", i); >> + } >> >> memset(&props, 0, sizeof(props)); >> props.type = BACKLIGHT_RAW; >> @@ -78,22 +95,34 @@ static int gpio_backlight_probe(struct platform_device *pdev) >> } >> >> /* Set the initial power state */ >> - if (!of_node || !of_node->phandle) >> + if (!of_node || !of_node->phandle) { >> /* Not booted with device tree or no phandle link to the node */ >> bl->props.power = def_value ? BACKLIGHT_POWER_ON >> - : BACKLIGHT_POWER_OFF; >> - else if (gpiod_get_value_cansleep(gbl->gpiod) == 0) >> - bl->props.power = BACKLIGHT_POWER_OFF; >> - else >> - bl->props.power = BACKLIGHT_POWER_ON; >> + : BACKLIGHT_POWER_OFF; >> + } else { >> + bool all_high = true; >> + >> + for (i = 0; i < gbl->num_gpios; i++) { >> + if (gpiod_get_value_cansleep(gbl->gpiods[i]) != 0) { > > Why is there a != here? > > >> + all_high = false; >> + break; >> + } >> + } >> + >> + bl->props.power = >> + all_high ? BACKLIGHT_POWER_ON : BACKLIGHT_POWER_OFF; >> + } >> >> bl->props.brightness = 1; >> >> init_brightness = backlight_get_brightness(bl); >> - ret = gpiod_direction_output(gbl->gpiod, init_brightness); >> - if (ret) { >> - dev_err(dev, "failed to set initial brightness\n"); >> - return ret; >> + >> + for (i = 0; i < gbl->num_gpios; i++) { >> + ret = gpiod_direction_output(gbl->gpiods[i], init_brightness); >> + if (ret) >> + return dev_err_probe(dev, ret, >> + "failed to set gpio %u direction\n", >> + i); >> } >> >> platform_set_drvdata(pdev, bl); > > > Daniel.