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    Subject[PATCH 3.16 157/346] drm/edid: Add 6 bpc quirk for display AEO model 0.
    3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mario Kleiner <mario.kleiner.de@gmail.com>

    commit e10aec652f31ec61d6a0b4d00d8ef8d2b66fa0fd upstream.

    Bugzilla https://bugzilla.kernel.org/show_bug.cgi?id=105331
    reports that the "AEO model 0" display is driven with 8 bpc
    without dithering by default, which looks bad because that
    panel is apparently a 6 bpc DP panel with faulty EDID.

    A fix for this was made by commit 013dd9e03872
    ("drm/i915/dp: fall back to 18 bpp when sink capability is unknown").

    That commit triggers new regressions in precision for DP->DVI and
    DP->VGA displays. A patch is out to revert that commit, but it will
    revert video output for the AEO model 0 panel to 8 bpc without
    dithering.

    The EDID 1.3 of that panel, as decoded from the xrandr output
    attached to that bugzilla bug report, is somewhat faulty, and beyond
    other problems also sets the "DFP 1.x compliant TMDS" bit, which
    according to DFP spec means to drive the panel with 8 bpc and
    no dithering in absence of other colorimetry information.

    Try to make the original bug reporter happy despite the
    faulty EDID by adding a quirk to mark that panel as 6 bpc,
    so 6 bpc output with dithering creates a nice picture.

    Tested by injecting the edid from the fdo bug into a DP connector
    via drm_kms_helper.edid_firmware and verifying the 6 bpc + dithering
    is selected.

    This patch should be backported to stable.

    Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
    Cc: Jani Nikula <jani.nikula@intel.com>
    Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: Dave Airlie <airlied@redhat.com>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/gpu/drm/drm_edid.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    --- a/drivers/gpu/drm/drm_edid.c
    +++ b/drivers/gpu/drm/drm_edid.c
    @@ -72,6 +72,8 @@
    #define EDID_QUIRK_FORCE_8BPC (1 << 8)
    /* Force 12bpc */
    #define EDID_QUIRK_FORCE_12BPC (1 << 9)
    +/* Force 6bpc */
    +#define EDID_QUIRK_FORCE_6BPC (1 << 10)

    struct detailed_mode_closure {
    struct drm_connector *connector;
    @@ -98,6 +100,9 @@ static struct edid_quirk {
    /* Unknown Acer */
    { "ACR", 2423, EDID_QUIRK_FIRST_DETAILED_PREFERRED },

    + /* AEO model 0 reports 8 bpc, but is a 6 bpc panel */
    + { "AEO", 0, EDID_QUIRK_FORCE_6BPC },
    +
    /* Belinea 10 15 55 */
    { "MAX", 1516, EDID_QUIRK_PREFER_LARGE_60 },
    { "MAX", 0x77e, EDID_QUIRK_PREFER_LARGE_60 },
    @@ -3667,6 +3672,9 @@ int drm_add_edid_modes(struct drm_connec

    drm_add_display_info(edid, &connector->display_info, connector);

    + if (quirks & EDID_QUIRK_FORCE_6BPC)
    + connector->display_info.bpc = 6;
    +
    if (quirks & EDID_QUIRK_FORCE_8BPC)
    connector->display_info.bpc = 8;

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