linux-kernel - Re: [PATCH v2 1/3] drm/panel: novatek-nt35560: Fix invalid return value

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Message-ID: <8cbbf5f8-84b4-43af-89b9-0ee4bc0a2591@linaro.org>
Date: Tue, 29 Jul 2025 11:17:10 +0200
From: neil.armstrong@...aro.org
To: Brigham Campbell <me@...ghamcampbell.com>,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 airlied@...il.com, simona@...ll.ch, linus.walleij@...aro.org,
 jessica.zhang@....qualcomm.com, sam@...nborg.org
Cc: dianders@...omium.org, skhan@...uxfoundation.org,
 linux-kernel-mentees@...ts.linux.dev, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] drm/panel: novatek-nt35560: Fix invalid return
 value

On 29/07/2025 07:44, Brigham Campbell wrote:
> Fix bug in nt35560_set_brightness() which causes the function to
> erroneously report an error. mipi_dsi_dcs_write() returns either a
> negative value when an error occurred or a positive number of bytes
> written when no error occurred. The buggy code reports an error under
> either condition.
> 
> Fixes: 7835ed6a9e86 ("drm/panel-sony-acx424akp: Modernize backlight handling")
> Signed-off-by: Brigham Campbell <me@...ghamcampbell.com>
> ---
>   drivers/gpu/drm/panel/panel-novatek-nt35560.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-novatek-nt35560.c b/drivers/gpu/drm/panel/panel-novatek-nt35560.c
> index 98f0782c8411..17898a29efe8 100644
> --- a/drivers/gpu/drm/panel/panel-novatek-nt35560.c
> +++ b/drivers/gpu/drm/panel/panel-novatek-nt35560.c
> @@ -161,7 +161,7 @@ static int nt35560_set_brightness(struct backlight_device *bl)
>   		par = 0x00;
>   		ret = mipi_dsi_dcs_write(dsi, MIPI_DCS_WRITE_CONTROL_DISPLAY,
>   					 &par, 1);
> -		if (ret) {
> +		if (ret < 0) {
>   			dev_err(nt->dev, "failed to disable display backlight (%d)\n", ret);
>   			return ret;
>   		}

Reviewed-by: Neil Armstrong <neil.armstrong@...aro.org>