linux-kernel - [PATCH] drm/i915/ilk: Disable SSC for DPLLs if we're not using it

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Date:	Mon, 23 May 2016 14:56:54 -0400
From:	Lyude <cpaul@...hat.com>
To:	intel-gfx@...ts.freedesktop.org
Cc:	Lyude <cpaul@...hat.com>, stable@...r.kernel.org,
	Daniel Vetter <daniel.vetter@...el.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org (open list:INTEL DRM DRIVERS (excluding
	Poulsbo, Moorestow...), linux-kernel@...r.kernel.org (open list))
Subject: [PATCH] drm/i915/ilk: Disable SSC for DPLLs if we're not using it

Thanks to Ville Syrjälä for pointing me towards the cause of this issue.

Unfortunately one of the sideaffects of having the refclk for a DPLL
set to SSC is that as long as it's set to SSC, the GPU will prevent us
from powering down any of the pipes or transcoders using it. A couple of
BIOSes, despite the fact they don't actually need it, enable SSC both in
PCH_DREF_CONTROL and on the DPLL configurations. This causes issues on
the first modeset, since we don't expect SSC to be left on and as a
result, can't successfully power down the pipes or the transcoders using
it. Here's an example from this Dell OptiPlex 990:

[drm:intel_modeset_init] SSC enabled by BIOS, overriding VBT which says disabled
[drm:intel_modeset_init] 2 display pipes available.
[drm:intel_update_cdclk] Current CD clock rate: 400000 kHz
[drm:intel_update_max_cdclk] Max CD clock rate: 400000 kHz
[drm:intel_update_max_cdclk] Max dotclock rate: 360000 kHz
vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
[drm:intel_crt_reset] crt adpa set to 0xf40000
[drm:intel_dp_init_connector] Adding DP connector on port C
[drm:intel_dp_aux_init] registering DPDDC-C bus for card0-DP-1
[drm:ironlake_init_pch_refclk] has_panel 0 has_lvds 0 has_ck505 0
[drm:ironlake_init_pch_refclk] Disabling SSC entirely
… later we try committing the first modeset …
[drm:intel_dump_pipe_config] [CRTC:26][modeset] config ffff88041b02e800 for pipe A
[drm:intel_dump_pipe_config] cpu_transcoder: A
…
[drm:intel_dump_pipe_config] dpll_hw_state: dpll: 0xc4016001, dpll_md: 0x0, fp0: 0x20e08, fp1: 0x30d07
[drm:intel_dump_pipe_config] planes on this crtc
[drm:intel_dump_pipe_config] STANDARD PLANE:23 plane: 0.0 idx: 0 enabled
[drm:intel_dump_pipe_config]     FB:42, fb = 800x600 format = 0x34325258
[drm:intel_dump_pipe_config]     scaler:0 src (0, 0) 800x600 dst (0, 0) 800x600
[drm:intel_dump_pipe_config] CURSOR PLANE:25 plane: 0.1 idx: 1 disabled, scaler_id = 0
[drm:intel_dump_pipe_config] STANDARD PLANE:27 plane: 0.1 idx: 2 disabled, scaler_id = 0
[drm:intel_get_shared_dpll] CRTC:26 allocated PCH DPLL A
[drm:intel_get_shared_dpll] using PCH DPLL A for pipe A
[drm:ilk_audio_codec_disable] Disable audio codec on port C, pipe A
[drm:intel_disable_pipe] disabling pipe A
------------[ cut here ]------------
WARNING: CPU: 1 PID: 130 at drivers/gpu/drm/i915/intel_display.c:1146 intel_disable_pipe+0x297/0x2d0 [i915]
pipe_off wait timed out
…
---[ end trace 94fc8aa03ae139e8 ]---
[drm:intel_dp_link_down]
[drm:ironlake_crtc_disable [i915]] *ERROR* failed to disable transcoder A

Later modesets succeed since they reset the DPLL's configuration anyway,
but this is enough to get stuck with a big fat warning in dmesg.

Normally we'd need to add some sort of ref counting mechanism to the
CRTCs so we avoid accidentally trying to shut off a shared resource, but
since ignore what the BIOS does anyway and we shut off the refclks
before any modesets, this workaround should suffice for now.

Cc: stable@...r.kernel.org
Signed-off-by: Lyude <cpaul@...hat.com>
---
 drivers/gpu/drm/i915/intel_display.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d500e6f..3fb6025 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8230,7 +8230,8 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_encoder *encoder;
-	u32 val, final;
+	int i;
+	u32 val, temp, final;
 	bool has_lvds = false;
 	bool has_cpu_edp = false;
 	bool has_panel = false;
@@ -8369,6 +8370,22 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
 		I915_WRITE(PCH_DREF_CONTROL, val);
 		POSTING_READ(PCH_DREF_CONTROL);
 		udelay(200);
+
+		/* Unset SSC as the refclk for all of the DPLLs */
+		for (i = 0; i < dev_priv->num_shared_dpll; i++) {
+			temp = I915_READ(PCH_DPLL(i));
+
+			if (!(temp & PLLB_REF_INPUT_SPREADSPECTRUMIN))
+				continue;
+
+			DRM_DEBUG_KMS("Disabling SSC refclk for %s\n",
+				      dev_priv->shared_dplls[i].name);
+
+			/* Change refclk to DREFCLK */
+			temp &= ~PLL_REF_INPUT_MASK;
+
+			I915_WRITE(PCH_DPLL(i), temp);
+		}
 	}
 
 	BUG_ON(val != final);
-- 
2.5.5