This is a note to let you know that I've just added the patch titled drm/i915: Refresh cached DP port register value on resume to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-i915-refresh-cached-dp-port-register-value-on-resume.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 664a84d2c77cbff2945ed7f96d08afbba42b6293 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@xxxxxxxxxxxxxxx> Date: Fri, 13 May 2016 20:53:56 +0300 Subject: drm/i915: Refresh cached DP port register value on resume MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> commit 664a84d2c77cbff2945ed7f96d08afbba42b6293 upstream. During hibernation the cached DP port register value will be left with whatever value we have there when we create the hibernation image. Currently that means the port (and eDP PLL) will be off in the cached value. However when we resume there is no guarantee that the value in the actual register will match the cached value. If i915 isn't loaded in the kernel that loads the hibernation image, the port may well be on (eg. left on by the BIOS). The encoder state readout does the right thing in this case and updates our encoder state to reflect the actual hardware state. However the post-resume modeset will then use the stale cached port register value in intel_dp_link_down() and potentially confuse the hardware. This was caught by the following assert WARNING: CPU: 3 PID: 5288 at ../drivers/gpu/drm/i915/intel_dp.c:2184 assert_edp_pll+0x99/0xa0 [i915] eDP PLL state assertion failure (expected on, current off) on account of the eDP PLL getting prematurely turned off when shutting down the port, since the DP_PLL_ENABLE bit wasn't set in the cached register value. Presumably I introduced this problem in commit 6fec76628333 ("drm/i915: Use intel_dp->DP in eDP PLL setup") as before that we didn't update the cached value after shuttting the port down. That's assuming the port got enabled at least once prior to hibernating. If that didn't happen then the cached value would still have been totally out of sync with reality (eg. first boot w/o eDP on, then hibernate, and then resume with eDP on). So, let's fix this properly and refresh the cached register value from the hardware register during resume. DDI platforms shouldn't use the cached value during port disable at least, so shouldn't have this particular issue. They might still have issues if we skip the initial modeset and then try to retrain the link or something. But untangling this DP vs. DDI mess is a bigger topic, so let's jut punt on DDI for now. Cc: Jani Nikula <jani.nikula@xxxxxxxxx> Fixes: 6fec76628333 ("drm/i915: Use intel_dp->DP in eDP PLL setup") Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> Link: http://patchwork.freedesktop.org/patch/msgid/1463162036-27931-1-git-send-email-ville.syrjala@xxxxxxxxxxxxxxx Reviewed-by: Imre Deak <imre.deak@xxxxxxxxx> (cherry picked from commit 64989ca4b27acb026b6496ec21e43bee66f86a5b) Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/i915/intel_dp.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- a/drivers/gpu/drm/i915/intel_dp.c +++ b/drivers/gpu/drm/i915/intel_dp.c @@ -5079,13 +5079,15 @@ static void intel_edp_panel_vdd_sanitize void intel_dp_encoder_reset(struct drm_encoder *encoder) { - struct intel_dp *intel_dp; + struct drm_i915_private *dev_priv = to_i915(encoder->dev); + struct intel_dp *intel_dp = enc_to_intel_dp(encoder); + + if (!HAS_DDI(dev_priv)) + intel_dp->DP = I915_READ(intel_dp->output_reg); if (to_intel_encoder(encoder)->type != INTEL_OUTPUT_EDP) return; - intel_dp = enc_to_intel_dp(encoder); - pps_lock(intel_dp); /* Patches currently in stable-queue which might be from ville.syrjala@xxxxxxxxxxxxxxx are queue-4.4/drm-i915-refresh-cached-dp-port-register-value-on-resume.patch queue-4.4/drm-i915-update-cdclk_freq-register-on-bdw-after-changing-cdclk-frequency.patch queue-4.4/drm-i915-ilk-don-t-disable-ssc-source-if-it-s-in-use.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html