On Sun, 2010-08-22 at 12:05 +0100, Chris Wilson wrote:
> Parse the EDID looking for a CEA-extension block that details whether
> the connected monitor has audio support over HDMI.
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Dave Airlie <airl...@redhat.com>
> ---
> drivers/gpu/drm/drm_edid.c | 27 +++++++++++++++++++++++++++
> include/drm/drm_crtc.h | 1 +
> 2 files changed, 28 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 96e9631..922b325 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -1326,6 +1326,33 @@ end:
> EXPORT_SYMBOL(drm_detect_hdmi_monitor);
>
> /**
> + * drm_edid_supports_audio - detect whether monitor supports audio.
> + * @edid: monitor EDID information
> + *
> + * Parse the CEA extension according to CEA-861-B.
> + * Return true if a monitor is connected that supports basic audio,
> + * false if not or unknown.
> + */
> +bool drm_edid_supports_audio(struct edid *edid)
> +{
> + int i;
> +
> + /* No EDID or EDID extensions */
> + if (edid == NULL || edid->extensions == 0)
> + return false;
> +
> + /* Find CEA extension */
> + for (i = 0; i < edid->extensions; i++) {
> + const char *edid_ext = (char *)edid + EDID_LENGTH * (i + 1);
> + if (edid_ext[0] == 0x02)
> + return edid_ext[3] & (1 << 6);
> + }
> +
> + return false;
> +}Nack, CEA is worse than that. What you have here is "does the zero'th CEA subblock's type field have this one bit set", which isn't a particularly meaningful thing to check. In particular this will say _any_ HDMI sink (with the HDMI vendor-specific block first in the CEA block collection) is an audio sink. You have to: - check that the CEA version field is high enough - scan for a vendor-specific data block - check that its OUI matches the HDMI association OUI - check that its length is 6 or greater so that you know the byte containing the audio feature field is present - check whether the top bit of that byte is set (indicating it can consume ACP, ISRC1, or ISRC2 packets) Refer to: http://cgit.freedesktop.org/xorg/app/edid-decode/tree/edid-decode.c#n564 in particular the calls down to cea_block() and then cea_hdmi_block(). - ajax
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