Bug#658662: drm/i915: no signal via DisplayPort on Sandy Bridge since Linux 3.2
Hi,
On Wed, Jul 04, 2012 at 10:39:49AM -0500, Jonathan Nieder wrote:
> Hi again,
>
> Peter Colberg wrote:
>
> > cd9dde44f47501394b9f0715b6a36a92aa74c0d0 is the first bad commit
>
> How about the attached patch --- does it work against the linux-3.2.y
> branch?
>
> Grateful,
> Jonathan
> From: Jesse Barnes <jbarnes@virtuousgeek.org>
> Date: Thu, 21 Jun 2012 15:13:50 -0700
> Subject: drm/i915: prefer wide & slow to fast & narrow in DP configs
>
> commit 684aaa646f90f5ee07799d52d0735625756e607b upstream.
>
> High frequency link configurations have the potential to cause trouble
> with long and/or cheap cables, so prefer slow and wide configurations
> instead. This patch has the potential to cause trouble for eDP
> configurations that lie about available lanes, so if we run into that we
> can make it conditional on eDP.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45801
> Tested-by: peter@colberg.org
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index d4c4937067fb..fae2050324bc 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -708,8 +708,8 @@ intel_dp_mode_fixup(struct drm_encoder *encoder, struct drm_display_mode *mode,
>
> bpp = adjusted_mode->private_flags & INTEL_MODE_DP_FORCE_6BPC ? 18 : 24;
>
> - for (lane_count = 1; lane_count <= max_lane_count; lane_count <<= 1) {
> - for (clock = 0; clock <= max_clock; clock++) {
> + for (clock = 0; clock <= max_clock; clock++) {
> + for (lane_count = 1; lane_count <= max_lane_count; lane_count <<= 1) {
> int link_avail = intel_dp_max_data_rate(intel_dp_link_clock(bws[clock]), lane_count);
>
> if (intel_dp_link_required(mode->clock, bpp)
> --
> 1.7.11.rc3
I tested upstream linux 3.2.23 with the above patch applied, and
the display is working fine, i.e. it comes up in maximum, native
resolution even after power-cycling the display.
Regards,
Peter
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