Re: [PATCH 2/2] drm/i915: constify validate_vbt in VBT parsing

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Apr 15, 2015 at 03:18:29PM +0300, Jani Nikula wrote:
> Make input and output of validate_vbt const, and fix the fallout. We
> shouldn't modify the VBT, so make the compiler help us here.
> 
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_bios.c | 50 ++++++++++++++++++++-------------------
>  1 file changed, 26 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
> index 4e3f3f427178..b1e047c5e594 100644
> --- a/drivers/gpu/drm/i915/intel_bios.c
> +++ b/drivers/gpu/drm/i915/intel_bios.c
> @@ -205,7 +205,7 @@ get_lvds_fp_timing(const struct bdb_header *bdb,
>  /* Try to find integrated panel data */
>  static void
>  parse_lfp_panel_data(struct drm_i915_private *dev_priv,
> -			    struct bdb_header *bdb)
> +		     const struct bdb_header *bdb)
>  {
>  	const struct bdb_lvds_options *lvds_options;
>  	const struct bdb_lvds_lfp_data *lvds_lfp_data;
> @@ -311,7 +311,8 @@ parse_lfp_panel_data(struct drm_i915_private *dev_priv,
>  }
>  
>  static void
> -parse_lfp_backlight(struct drm_i915_private *dev_priv, struct bdb_header *bdb)
> +parse_lfp_backlight(struct drm_i915_private *dev_priv,
> +		    const struct bdb_header *bdb)
>  {
>  	const struct bdb_lfp_backlight_data *backlight_data;
>  	const struct bdb_lfp_backlight_data_entry *entry;
> @@ -349,7 +350,7 @@ parse_lfp_backlight(struct drm_i915_private *dev_priv, struct bdb_header *bdb)
>  /* Try to find sdvo panel data */
>  static void
>  parse_sdvo_panel_data(struct drm_i915_private *dev_priv,
> -		      struct bdb_header *bdb)
> +		      const struct bdb_header *bdb)
>  {
>  	const struct lvds_dvo_timing *dvo_timing;
>  	struct drm_display_mode *panel_fixed_mode;
> @@ -403,7 +404,7 @@ static int intel_bios_ssc_frequency(struct drm_device *dev,
>  
>  static void
>  parse_general_features(struct drm_i915_private *dev_priv,
> -		       struct bdb_header *bdb)
> +		       const struct bdb_header *bdb)
>  {
>  	struct drm_device *dev = dev_priv->dev;
>  	const struct bdb_general_features *general;
> @@ -429,7 +430,7 @@ parse_general_features(struct drm_i915_private *dev_priv,
>  
>  static void
>  parse_general_definitions(struct drm_i915_private *dev_priv,
> -			  struct bdb_header *bdb)
> +			  const struct bdb_header *bdb)
>  {
>  	const struct bdb_general_definitions *general;
>  
> @@ -456,7 +457,7 @@ child_device_ptr(const struct bdb_general_definitions *p_defs, int i)
>  
>  static void
>  parse_sdvo_device_mapping(struct drm_i915_private *dev_priv,
> -			  struct bdb_header *bdb)
> +			  const struct bdb_header *bdb)
>  {
>  	struct sdvo_device_mapping *p_mapping;
>  	const struct bdb_general_definitions *p_defs;
> @@ -546,7 +547,7 @@ parse_sdvo_device_mapping(struct drm_i915_private *dev_priv,
>  
>  static void
>  parse_driver_features(struct drm_i915_private *dev_priv,
> -		       struct bdb_header *bdb)
> +		      const struct bdb_header *bdb)
>  {
>  	const struct bdb_driver_features *driver;
>  
> @@ -572,7 +573,7 @@ parse_driver_features(struct drm_i915_private *dev_priv,
>  }
>  
>  static void
> -parse_edp(struct drm_i915_private *dev_priv, struct bdb_header *bdb)
> +parse_edp(struct drm_i915_private *dev_priv, const struct bdb_header *bdb)
>  {
>  	const struct bdb_edp *edp;
>  	const struct edp_power_seq *edp_pps;
> @@ -679,7 +680,7 @@ parse_edp(struct drm_i915_private *dev_priv, struct bdb_header *bdb)
>  }
>  
>  static void
> -parse_psr(struct drm_i915_private *dev_priv, struct bdb_header *bdb)
> +parse_psr(struct drm_i915_private *dev_priv, const struct bdb_header *bdb)
>  {
>  	const struct bdb_psr *psr;
>  	const struct psr_table *psr_table;
> @@ -790,7 +791,7 @@ static u8 *goto_next_sequence(u8 *data, int *size)
>  }
>  
>  static void
> -parse_mipi(struct drm_i915_private *dev_priv, struct bdb_header *bdb)
> +parse_mipi(struct drm_i915_private *dev_priv, const struct bdb_header *bdb)
>  {
>  	const struct bdb_mipi_config *start;
>  	const struct bdb_mipi_sequence *sequence;
> @@ -941,7 +942,7 @@ err:
>  }
>  
>  static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
> -			   struct bdb_header *bdb)
> +			   const struct bdb_header *bdb)
>  {
>  	union child_device_config *it, *child = NULL;
>  	struct ddi_vbt_port_info *info = &dev_priv->vbt.ddi_port_info[port];
> @@ -1043,7 +1044,7 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
>  }
>  
>  static void parse_ddi_ports(struct drm_i915_private *dev_priv,
> -			    struct bdb_header *bdb)
> +			    const struct bdb_header *bdb)
>  {
>  	struct drm_device *dev = dev_priv->dev;
>  	enum port port;
> @@ -1063,7 +1064,7 @@ static void parse_ddi_ports(struct drm_i915_private *dev_priv,
>  
>  static void
>  parse_device_mapping(struct drm_i915_private *dev_priv,
> -		       struct bdb_header *bdb)
> +		     const struct bdb_header *bdb)
>  {
>  	const struct bdb_general_definitions *p_defs;
>  	const union child_device_config *p_child;
> @@ -1193,19 +1194,21 @@ static const struct dmi_system_id intel_no_opregion_vbt[] = {
>  	{ }
>  };
>  
> -static struct bdb_header *validate_vbt(char *base, size_t size,
> -				       struct vbt_header *vbt,
> -				       const char *source)
> +const static struct bdb_header *validate_vbt(const void *_base, size_t size,
> +					     const void *_vbt,
> +					     const char *source)
>  {
> +	const char *base = _base;
> +	const struct vbt_header *vbt = _vbt;
>  	size_t offset;
> -	struct bdb_header *bdb;
> +	const struct bdb_header *bdb;
>  
>  	if (vbt == NULL) {
>  		DRM_DEBUG_DRIVER("VBT signature missing\n");
>  		return NULL;
>  	}
>  
> -	offset = (char *)vbt - base;
> +	offset = (const char *)vbt - base;

I believe we're using void* arithmetic elsewhere already, so maybe just
use it here too and avoid the duplicated variables?

>  	if (offset + sizeof(struct vbt_header) > size) {
>  		DRM_DEBUG_DRIVER("VBT header incomplete\n");
>  		return NULL;
> @@ -1222,7 +1225,7 @@ static struct bdb_header *validate_vbt(char *base, size_t size,
>  		return NULL;
>  	}
>  
> -	bdb = (struct bdb_header *)(base + offset);
> +	bdb = (const struct bdb_header *)(base + offset);
>  	if (offset + bdb->bdb_size > size) {
>  		DRM_DEBUG_DRIVER("BDB incomplete\n");
>  		return NULL;
> @@ -1247,7 +1250,7 @@ intel_parse_bios(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct pci_dev *pdev = dev->pdev;
> -	struct bdb_header *bdb = NULL;
> +	const struct bdb_header *bdb = NULL;
>  	u8 __iomem *bios = NULL;
>  
>  	if (HAS_PCH_NOP(dev))
> @@ -1257,9 +1260,8 @@ intel_parse_bios(struct drm_device *dev)
>  
>  	/* XXX Should this validation be moved to intel_opregion.c? */
>  	if (!dmi_check_system(intel_no_opregion_vbt) && dev_priv->opregion.vbt)
> -		bdb = validate_vbt((char *)dev_priv->opregion.header, OPREGION_SIZE,
> -				   (struct vbt_header *)dev_priv->opregion.vbt,
> -				   "OpRegion");
> +		bdb = validate_vbt(dev_priv->opregion.header, OPREGION_SIZE,
> +				   dev_priv->opregion.vbt, "OpRegion");
>  
>  	if (bdb == NULL) {
>  		size_t i, size;
> @@ -1272,7 +1274,7 @@ intel_parse_bios(struct drm_device *dev)
>  		for (i = 0; i + 4 < size; i++) {
>  			if (memcmp(bios + i, "$VBT", 4) == 0) {
>  				bdb = validate_vbt(bios, size,
> -						   (struct vbt_header *)(bios + i),
> +						   bios + i,
>  						   "PCI ROM");
>  				break;
>  			}
> -- 
> 2.1.4
> 
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-- 
Ville Syrjälä
Intel OTC
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