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    SubjectRe: radeon + DVI->mDP converter + mDP display blank screen issue since 3.0
    On Fri, Mar 23, 2012 at 10:59:27AM -0400, Alex Deucher wrote:

    > > Since Linux 3.0, a system with a Radeon HD 5450 (1002:68f9) connected
    > > to a 27" Apple LED cinema display via an Atlona AT-DP400 Dual Link DVI
    > > to Mini DisplayPort converter has started to stop giving screen
    > > output on switching from text mode to graphical framebuffer during
    > > system startup.
    > >
    > > I finally had some time to look at this, and it seems to have stopped
    > > working after this commit:
    > >
    > >        commit df271bec805b42527d864777ed035fcbb42e76c0
    > >        Author: Alex Deucher <alexdeucher@gmail.com>
    > >        Date:   Fri May 20 04:34:15 2011 -0400
    > >
    > >            drm/radeon/kms: properly handle bpc >8 in atom command tables
    > >
    > >            Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
    > >            Signed-off-by: Dave Airlie <airlied@redhat.com>
    > >
    > > ...and with the patch below (i.e. reverting part of the commit above)
    > > applied to 3.3 I get screen output again.
    > >
    > > Even though the monitor seems to have an 8 bit panel, it reports 10
    > > bits per channel in its EDID:
    > >
    > >        [...]
    > >        Manufacturer: APP Model 9226 Serial Number 41959462
    > >        Made week 38 of 2010
    > >        EDID version: 1.4
    > >        Digital display
    > >        10 bits per primary color channel
    > >        DisplayPort interface
    > >        Maximum image size: 60 cm x 34 cm
    > >        [...]
    > >
    > > The (active, dual link) DVI->mDP converter spec sheet says it supports
    > > 24 bit color, and I'm guessing that it can't deal with 30.  Is the
    > > converter at fault here for passing through the EDID unchanged?
    > >
    > > Also, what would be the right way to handle this, a kernel command
    > > line or module option to limit color depth or something like that?
    > > ("Buy a video card with DP output." is a valid answer, I suppose.)
    > >
    > > I have no clue at all about graphics, and I have no idea whatsoever
    > > what I'm doing here, but I just wanted to post this somewhere for
    > > Google to find in case someone else runs into this!
    >
    > I've inquired with out display team on how to best handle this. In
    > the meantime, it's probably best to just default to 8 bpc. Does the
    > attached patch fix your issue?

    I've been using the patch below in a custom Fedora 17 kernel RPM, and
    that seems to fix the issue. Your patch seems to be a superset of
    this patch, so logically, your patch should do the trick as well. :)


    thanks,
    Lennert


    diff -up linux-3.3.0-1.fc17.x86_64/drivers/gpu/drm/radeon/atombios_crtc.c.orig linux-3.3.0-1.fc17.x86_64/drivers/gpu/drm/radeon/atombios_crtc.c
    --- linux-3.3.0-1.fc17.x86_64/drivers/gpu/drm/radeon/atombios_crtc.c.orig 2012-03-22 14:52:20.538854547 +0100
    +++ linux-3.3.0-1.fc17.x86_64/drivers/gpu/drm/radeon/atombios_crtc.c 2012-03-22 14:55:39.740794113 +0100
    @@ -550,8 +550,6 @@ static u32 atombios_adjust_pll(struct dr
    if (encoder->crtc == crtc) {
    radeon_encoder = to_radeon_encoder(encoder);
    connector = radeon_get_connector_for_encoder(encoder);
    - if (connector && connector->display_info.bpc)
    - bpc = connector->display_info.bpc;
    encoder_mode = atombios_get_encoder_mode(encoder);
    is_duallink = radeon_dig_monitor_is_duallink(encoder, mode->clock);
    if ((radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT | ATOM_DEVICE_DFP_SUPPORT)) ||
    @@ -922,7 +920,6 @@ static void atombios_crtc_set_pll(struct
    struct radeon_connector_atom_dig *dig_connector =
    radeon_connector->con_priv;
    int dp_clock;
    - bpc = connector->display_info.bpc;

    switch (encoder_mode) {
    case ATOM_ENCODER_MODE_DP_MST:


    > From 22ca454eb749968f266d6788a5f4778acc08cc66 Mon Sep 17 00:00:00 2001
    > From: Alex Deucher <alexander.deucher@amd.com>
    > Date: Fri, 23 Mar 2012 10:54:45 -0400
    > Subject: [PATCH] drm/radeon/kms/atom: force bpc to 8 for now
    >
    > Using the bpc (bits per color) specified by the monitor
    > can cause problems in some cases. Until we get a better
    > handle on how to deal with those cases, just use a bpc of 8.
    >
    > Reported-by: Lennert Buytenhek <buytenh@wantstofly.org>
    > Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
    > Cc: stable@kernel.org
    > ---
    > drivers/gpu/drm/radeon/atombios_crtc.c | 8 +++++---
    > drivers/gpu/drm/radeon/atombios_dp.c | 3 +++
    > drivers/gpu/drm/radeon/atombios_encoders.c | 4 ++--
    > 3 files changed, 10 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/gpu/drm/radeon/atombios_crtc.c b/drivers/gpu/drm/radeon/atombios_crtc.c
    > index 083b3ea..b5ff1f7 100644
    > --- a/drivers/gpu/drm/radeon/atombios_crtc.c
    > +++ b/drivers/gpu/drm/radeon/atombios_crtc.c
    > @@ -588,8 +588,8 @@ static u32 atombios_adjust_pll(struct drm_crtc *crtc,
    > if (encoder->crtc == crtc) {
    > radeon_encoder = to_radeon_encoder(encoder);
    > connector = radeon_get_connector_for_encoder(encoder);
    > - if (connector && connector->display_info.bpc)
    > - bpc = connector->display_info.bpc;
    > + /* if (connector && connector->display_info.bpc)
    > + bpc = connector->display_info.bpc; */
    > encoder_mode = atombios_get_encoder_mode(encoder);
    > is_duallink = radeon_dig_monitor_is_duallink(encoder, mode->clock);
    > if ((radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT | ATOM_DEVICE_DFP_SUPPORT)) ||
    > @@ -965,7 +965,9 @@ static void atombios_crtc_set_pll(struct drm_crtc *crtc, struct drm_display_mode
    > struct radeon_connector_atom_dig *dig_connector =
    > radeon_connector->con_priv;
    > int dp_clock;
    > - bpc = connector->display_info.bpc;
    > +
    > + /* if (connector->display_info.bpc)
    > + bpc = connector->display_info.bpc; */
    >
    > switch (encoder_mode) {
    > case ATOM_ENCODER_MODE_DP_MST:
    > diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
    > index 6c62be2..c57d856 100644
    > --- a/drivers/gpu/drm/radeon/atombios_dp.c
    > +++ b/drivers/gpu/drm/radeon/atombios_dp.c
    > @@ -405,10 +405,13 @@ static void dp_get_adjust_train(u8 link_status[DP_LINK_STATUS_SIZE],
    > /* get bpc from the EDID */
    > static int convert_bpc_to_bpp(int bpc)
    > {
    > +#if 0
    > if (bpc == 0)
    > return 24;
    > else
    > return bpc * 3;
    > +#endif
    > + return 24;
    > }
    >
    > /* get the max pix clock supported by the link rate and lane num */
    > diff --git a/drivers/gpu/drm/radeon/atombios_encoders.c b/drivers/gpu/drm/radeon/atombios_encoders.c
    > index 468b874..e607c4d 100644
    > --- a/drivers/gpu/drm/radeon/atombios_encoders.c
    > +++ b/drivers/gpu/drm/radeon/atombios_encoders.c
    > @@ -541,7 +541,7 @@ atombios_dig_encoder_setup(struct drm_encoder *encoder, int action, int panel_mo
    > dp_clock = dig_connector->dp_clock;
    > dp_lane_count = dig_connector->dp_lane_count;
    > hpd_id = radeon_connector->hpd.hpd;
    > - bpc = connector->display_info.bpc;
    > + /* bpc = connector->display_info.bpc; */
    > }
    >
    > /* no dig encoder assigned */
    > @@ -1159,7 +1159,7 @@ atombios_external_encoder_setup(struct drm_encoder *encoder,
    > dp_lane_count = dig_connector->dp_lane_count;
    > connector_object_id =
    > (radeon_connector->connector_object_id & OBJECT_ID_MASK) >> OBJECT_ID_SHIFT;
    > - bpc = connector->display_info.bpc;
    > + /* bpc = connector->display_info.bpc; */
    > }
    >
    > memset(&args, 0, sizeof(args));
    > --
    > 1.7.7.5
    >
    --
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