Re: [PATCH 2/2] drm/ssd130x: Add per-family update backlight logic

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Multi-byte hardware command sequences can interleave during concurrent display and backlight updates, corrupting the panel state.
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--- Patch [2]: [PATCH 2/2] drm/ssd130x: Add per-family update backlight logic ---
commit 3c6fc209e783670f32fed55dedcfe0a2a66ad662
Author: Amit Barzilai <amit.barzilai22@gmail.com>

drm/ssd130x: Add per-family update backlight logic
    
This commit adds per-family backlight update logic to support SSD133x panels,
which require a three-channel contrast update sequence instead of a single
global contrast command.

> diff --git a/drivers/gpu/drm/solomon/ssd130x.c b/drivers/gpu/drm/solomon/ssd130x.c
> index f49e5245b2160..0b0fc6fe3df23 100644
> --- a/drivers/gpu/drm/solomon/ssd130x.c
> +++ b/drivers/gpu/drm/solomon/ssd130x.c
> @@ -1711,8 +1711,25 @@ static int ssd130x_update_bl(struct backlight_device *bdev)
>  	return 0;
>  }
>  
> -static const struct backlight_ops ssd130xfb_bl_ops = {
> -	.update_status	= ssd130x_update_bl,
> +static int ssd133x_update_bl(struct backlight_device *bdev)
> +{
> +	struct ssd130x_device *ssd130x = bl_get_data(bdev);
> +
> +	ssd130x->contrast = backlight_get_brightness(bdev);
> +
> +	return ssd133x_set_contrast(ssd130x, ssd130x->contrast);
> +}

[Severity: High]
This is a pre-existing issue, but does this newly added function exacerbate a
race condition with concurrent DRM atomic plane updates?

When a backlight sysfs brightness update runs concurrently with a DRM atomic
plane update, both paths invoke regmap_write() repeatedly to send multi-byte
sequences. Since regmap_write() only locks internally for a single byte, there
appears to be no driver-level mutex to serialize the entire command sequence.

The newly added ssd133x_update_bl() sends a 7-command multi-byte sequence via
ssd133x_set_contrast() and ssd130x_run_cmd_seq() without driver-level locks.
Similarly, the existing ssd130x_update_bl() function splits a 2-byte command
across two separate ssd130x_write_cmd() calls.

Could these multi-byte hardware command sequences interleave during concurrent
display and backlight updates, and potentially corrupt the panel's hardware
state machine?

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260729053054.29374-1-amit.barzilai22@gmail.com?part=2