Re: [PATCH 07/10] drm/i915: Allow 27 bytes child_dev for VBT <109

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 14 Dec 2015, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> My 85x has VBT version 108 which has a child dev size of 27 bytes.
> Let's allow that without printing an error.
>
> We still want to reject the actual parsin since for that we need
> the child device size to be at least 33 bytes. So we should still
> check for that, but let's make it print a debug message only instead
> of an error.
>
> While at it, toss in a BUILD_BUG_ON() to verify our struct
> old_child_dev_config is in fact 33 bytes.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

This is scary stuff, but

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

as far as the code goes. I don't have the history books to check this
against.

> ---
>  drivers/gpu/drm/i915/intel_bios.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
> index 070470fe9a91..770b825dabc0 100644
> --- a/drivers/gpu/drm/i915/intel_bios.c
> +++ b/drivers/gpu/drm/i915/intel_bios.c
> @@ -1089,7 +1089,10 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
>  		DRM_DEBUG_KMS("No general definition block is found, no devices defined.\n");
>  		return;
>  	}
> -	if (bdb->version < 195) {
> +	if (bdb->version < 109) {
> +		expected_size = 27;
> +	} else if (bdb->version < 195) {
> +		BUILD_BUG_ON(sizeof(struct old_child_dev_config) != 33);
>  		expected_size = sizeof(struct old_child_dev_config);
>  	} else if (bdb->version == 195) {
>  		expected_size = 37;
> @@ -1102,18 +1105,18 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
>  				 bdb->version, expected_size);
>  	}
>  
> -	/* The legacy sized child device config is the minimum we need. */
> -	if (p_defs->child_dev_size < sizeof(struct old_child_dev_config)) {
> -		DRM_ERROR("Child device config size %u is too small.\n",
> -			  p_defs->child_dev_size);
> -		return;
> -	}
> -
>  	/* Flag an error for unexpected size, but continue anyway. */
>  	if (p_defs->child_dev_size != expected_size)
>  		DRM_ERROR("Unexpected child device config size %u (expected %u for VBT version %u)\n",
>  			  p_defs->child_dev_size, expected_size, bdb->version);
>  
> +	/* The legacy sized child device config is the minimum we need. */
> +	if (p_defs->child_dev_size < sizeof(struct old_child_dev_config)) {
> +		DRM_DEBUG_KMS("Child device config size %u is too small.\n",
> +			      p_defs->child_dev_size);
> +		return;
> +	}
> +
>  	/* get the block size of general definitions */
>  	block_size = get_blocksize(p_defs);
>  	/* get the number of child device */

-- 
Jani Nikula, Intel Open Source Technology Center
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