Re: [PATCH] drm/edid: reduce update_display_info() stack usage

[Jani Nikula]

On Tue, 13 Oct 2026, Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> The drm_parse_cea_ext() calls into nine individual parser functions
> based on the data format. If all of those get inlined and KASAN_STACK
> is enabled, this can explode the combined stack usage beyond a
> reasonable amount:
>
> drivers/gpu/drm/drm_edid.c: In function 'update_display_info':
> drivers/gpu/drm/drm_edid.c:7040:1: error: the frame size of 1888 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]
>  7040 | }
>       | ^
>
> Mark all of the individual parser functions as noinline_for_stack
> to avoid this and keep their stack frames separate. This reduces
> the stack usage for update_display_info/drm_parse_cea_ext to
> a more manageable 744 bytes, while each parser only adds at most
> 200 bytes on top.

Is there really no way to tell the compiler to not do silly things in a
more generic way?

BR,
Jani.


>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  drivers/gpu/drm/drm_edid.c | 31 +++++++++++++++++--------------
>  1 file changed, 17 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 3148038747b6..913a8bbe8894 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -5341,8 +5341,9 @@ static int edid_hfeeodb_extension_block_count(const struct edid *edid)
>   * etc). For example, if the bit 0 in bitmap is set, first mode in VDB can
>   * support YCBCR420 output too.
>   */
> -static void parse_cta_y420cmdb(struct drm_connector *connector,
> -			       const struct cea_db *db, u64 *y420cmdb_map)
> +static noinline_for_stack void
> +parse_cta_y420cmdb(struct drm_connector *connector, const struct cea_db *db,
> +		   u64 *y420cmdb_map)
>  {
>  	struct drm_display_info *info = &connector->display_info;
>  	int i, map_len = cea_db_payload_len(db) - 1;
> @@ -5515,7 +5516,7 @@ static uint8_t hdr_metadata_type(const u8 *edid_ext)
>  		BIT(HDMI_STATIC_METADATA_TYPE1);
>  }
>  
> -static void
> +static noinline_for_stack void
>  drm_parse_hdr_metadata_block(struct drm_connector *connector, const u8 *db)
>  {
>  	struct hdr_static_metadata *hdr_metadata =
> @@ -6070,7 +6071,8 @@ drm_default_rgb_quant_range(const struct drm_display_mode *mode)
>  EXPORT_SYMBOL(drm_default_rgb_quant_range);
>  
>  /* CTA-861 Video Data Block (CTA VDB) */
> -static void parse_cta_vdb(struct drm_connector *connector, const struct cea_db *db)
> +static noinline_for_stack void
> +parse_cta_vdb(struct drm_connector *connector, const struct cea_db *db)
>  {
>  	struct drm_display_info *info = &connector->display_info;
>  	int i, vic_index, len = cea_db_payload_len(db);
> @@ -6136,8 +6138,8 @@ static bool cta_vdb_has_vic(const struct drm_connector *connector, u8 vic)
>  }
>  
>  /* CTA-861-H YCbCr 4:2:0 Video Data Block (CTA Y420VDB) */
> -static void parse_cta_y420vdb(struct drm_connector *connector,
> -			      const struct cea_db *db)
> +static noinline_for_stack void
> +parse_cta_y420vdb(struct drm_connector *connector, const struct cea_db *db)
>  {
>  	struct drm_display_info *info = &connector->display_info;
>  	struct drm_hdmi_info *hdmi = &info->hdmi;
> @@ -6155,7 +6157,8 @@ static void parse_cta_y420vdb(struct drm_connector *connector,
>  	}
>  }
>  
> -static void drm_parse_vcdb(struct drm_connector *connector, const u8 *db)
> +static noinline_for_stack void
> +drm_parse_vcdb(struct drm_connector *connector, const u8 *db)
>  {
>  	struct drm_display_info *info = &connector->display_info;
>  
> @@ -6310,8 +6313,8 @@ static void drm_parse_dsc_info(struct drm_hdmi_dsc_cap *hdmi_dsc,
>  }
>  
>  /* Sink Capability Data Structure */
> -static void drm_parse_hdmi_forum_scds(struct drm_connector *connector,
> -				      const u8 *hf_scds)
> +static noinline_for_stack void
> +drm_parse_hdmi_forum_scds(struct drm_connector *connector, const u8 *hf_scds)
>  {
>  	struct drm_display_info *info = &connector->display_info;
>  	struct drm_hdmi_info *hdmi = &info->hdmi;
> @@ -6451,7 +6454,7 @@ static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
>  }
>  
>  /* HDMI Vendor-Specific Data Block (HDMI VSDB, H14b-VSDB) */
> -static void
> +static noinline_for_stack void
>  drm_parse_hdmi_vsdb_video(struct drm_connector *connector, const u8 *db)
>  {
>  	struct drm_display_info *info = &connector->display_info;
> @@ -6486,8 +6489,8 @@ drm_parse_hdmi_vsdb_video(struct drm_connector *connector, const u8 *db)
>   * See EDID extension for head-mounted and specialized monitors, specified at:
>   * https://docs.microsoft.com/en-us/windows-hardware/drivers/display/specialized-monitors-edid-extension
>   */
> -static void drm_parse_microsoft_vsdb(struct drm_connector *connector,
> -				     const u8 *db)
> +static noinline_for_stack void
> +drm_parse_microsoft_vsdb(struct drm_connector *connector, const u8 *db)
>  {
>  	struct drm_display_info *info = &connector->display_info;
>  	u8 version = db[4];
> @@ -6558,8 +6561,8 @@ static void drm_parse_amd_vsdb_v3(struct drm_display_info *info,
>  	info->amd_vsdb.max_frame_rate = max_frame_rate;
>  }
>  
> -static void drm_parse_amd_vsdb(struct drm_connector *connector,
> -			       const struct cea_db *db)
> +static noinline_for_stack void
> +drm_parse_amd_vsdb(struct drm_connector *connector, const struct cea_db *db)
>  {
>  	struct drm_display_info *info = &connector->display_info;
>  	const u8 *data = cea_db_data(db);

-- 
Jani Nikula, Intel