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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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