Re: [PATCH v4 5/5] drm/bridge: it6505: Don't reject audio hw_params without an encoder

[sashiko-bot@kernel.org]

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

Pre-existing issues:
- [High] Division by zero kernel panic in `__it6505_enable_audio()` when `REG_AUDIO_INPUT_FREQ` reads 0.
--

--- Patch [5]: [PATCH v4 5/5] drm/bridge: it6505: Don't reject audio hw_params without an encoder ---
commit ce61845cbb90df0a24913039e8ff09c7c4ff53e7
Author: Daniel Golle <daniel@makrotopia.org>

drm/bridge: it6505: Don't reject audio hw_params without an encoder
    
This commit drops the encoder check in it6505_audio_setup_hw_params() to
ensure stream parameters are always cached, even when no display is attached.
It also moves the application of audio parameter defaults to probe time.

> diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
> index 6bb5db565ccac..e01d57b0166a8 100644
> --- a/drivers/gpu/drm/bridge/ite-it6505.c
> +++ b/drivers/gpu/drm/bridge/ite-it6505.c
> @@ -3004,9 +2994,6 @@ static int it6505_audio_setup_hw_params(struct it6505 *it6505,
>  			     params->sample_rate, params->sample_width,
>  			     params->cea.channels);
>  
> -	if (!it6505->bridge.encoder)
> -		return -ENODEV;
> -

[ ... ]

[Severity: High]
This is a pre-existing issue, but can this code cause a division by zero kernel
panic?

Looking at __it6505_enable_audio() in drivers/gpu/drm/bridge/ite-it6505.c, 
if it6505_read() returns 0 (e.g. if no I2S clock is present or the read fails), 
regbe is used as a denominator:

	regbe = it6505_read(it6505, REG_AUDIO_INPUT_FREQ);
	DRM_DEV_DEBUG_DRIVER(dev, "regbe:0x%02x audio input fs: %d.%d kHz",
			     regbe, 6750 / regbe, (6750 % regbe) * 10 / regbe);

When DRM debugging is enabled, this would evaluate the arguments and divide by
zero. Should there be a check to ensure regbe is non-zero before it is used in
the DRM_DEV_DEBUG_DRIVER macro?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1784681487.git.daniel@makrotopia.org?part=5