Hi Ville,
On Mon, 2 Sep 2019 16:15:45 +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> CEA ext block revisions 1 and 2 do not contain the data block
> collection. Instead that section of the extension block is
> marked as reserved for 8 byte timing descriptors. Revision 3
> changed it to contain the CEA data block collection instead.
>
> Most places that iterate the data blocks already check for
> revision >= 3, but drm_detect_hdmi_monitor() and
> drm_detect_monitor_audio() do not. So in theory when encountering
> rev 1 or 2 CEA extension block they could end up misinterpreting
> whatever data is in the reserved section as CEA data blocks.
>
> Let's have cea_db_offsets() do the revision check so that the
> callers don't even have worry about it.
>
> Cc: Jean Delvare <jdelvare@xxxxxxx>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_edid.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 82a4ceed3fcf..7b3072fc550b 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -3690,6 +3690,9 @@ cea_revision(const u8 *cea)
> static int
> cea_db_offsets(const u8 *cea, int *start, int *end)
> {
> + if (cea_revision(cea) < 3)
> + return -ENOTSUPP;
> +
> /* DisplayID CTA extension blocks and top-level CEA EDID
> * block header definitions differ in the following bytes:
> * 1) Byte 2 of the header specifies length differently,
Reviewed-by: Jean Delvare <jdelvare@xxxxxxx>
I like it, but then we need a subsequent patch to remove the now
redundant checks in add_cea_modes(), drm_edid_to_eld(),
drm_edid_to_sad() and drm_edid_to_speaker_allocation().
These last 2 functions are the ones my own patch modifies, so some care
is needed. If cea_db_offsets() now returns an error when CEA revisions
< 3, then these functions want to return 0 in that case (otherwise you
effectively undo the change I proposed).
By the way, both functions issue a debug message "SAD: invalid data
block offsets" when cea_db_offsets() returns an error, which becomes
misleading after your change. I think we want to move this message
inside cea_db_offsets() and only print it in the -ERANGE case.
--
Jean Delvare
SUSE L3 Support
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