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Subject[PATCH v2] drm/i915/ilk: Don't disable SSC source if it's in use
Date
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 enable SSC in both PCH_DREF_CONTROL and in 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.

A better solution would be to add refcounts for the SSC source, but for
now leaving the source clock on should suffice.

Changes since v1:
- Leave the SSC source clock on instead of just shutting it off on all
of the DPLL configurations.

Cc: stable@vger.kernel.org
Signed-off-by: Lyude <cpaul@redhat.com>
---
Sorry about that! I misread danvet's suggestion as "disable the SSC" instead of
"don't disable the SSC".

drivers/gpu/drm/i915/intel_display.c | 47 +++++++++++++++++++++++++++---------
1 file changed, 35 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d500e6f..dff8511 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8230,12 +8230,14 @@ 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;
bool has_ck505 = false;
bool can_ssc = false;
+ bool using_ssc_source = false;

/* We need to take the global config into account */
for_each_intel_encoder(dev, encoder) {
@@ -8283,9 +8285,26 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
else
final |= DREF_NONSPREAD_SOURCE_ENABLE;

- final &= ~DREF_SSC_SOURCE_MASK;
final &= ~DREF_CPU_SOURCE_OUTPUT_MASK;
- final &= ~DREF_SSC1_ENABLE;
+
+ /* Check if any DPLLs are using the SSC source */
+ for (i = 0; i < dev_priv->num_shared_dpll; i++) {
+ temp = I915_READ(PCH_DPLL(i));
+
+ if (!(temp & DPLL_VCO_ENABLE))
+ continue;
+
+ if ((temp & PLL_REF_INPUT_MASK) ==
+ PLLB_REF_INPUT_SPREADSPECTRUMIN) {
+ using_ssc_source = true;
+ break;
+ }
+ }
+
+ if (!using_ssc_source) {
+ final &= ~DREF_SSC_SOURCE_MASK;
+ final &= ~DREF_SSC1_ENABLE;
+ }

if (has_panel) {
final |= DREF_SSC_SOURCE_ENABLE;
@@ -8348,7 +8367,7 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
POSTING_READ(PCH_DREF_CONTROL);
udelay(200);
} else {
- DRM_DEBUG_KMS("Disabling SSC entirely\n");
+ DRM_DEBUG_KMS("Disabling SSC CPU output\n");

val &= ~DREF_CPU_SOURCE_OUTPUT_MASK;

@@ -8359,16 +8378,20 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
POSTING_READ(PCH_DREF_CONTROL);
udelay(200);

- /* Turn off the SSC source */
- val &= ~DREF_SSC_SOURCE_MASK;
- val |= DREF_SSC_SOURCE_DISABLE;
+ if (!using_ssc_source) {
+ DRM_DEBUG_KMS("Disabling SSC source\n");

- /* Turn off SSC1 */
- val &= ~DREF_SSC1_ENABLE;
+ /* Turn off the SSC source */
+ val &= ~DREF_SSC_SOURCE_MASK;
+ val |= DREF_SSC_SOURCE_DISABLE;

- I915_WRITE(PCH_DREF_CONTROL, val);
- POSTING_READ(PCH_DREF_CONTROL);
- udelay(200);
+ /* Turn off SSC1 */
+ val &= ~DREF_SSC1_ENABLE;
+
+ I915_WRITE(PCH_DREF_CONTROL, val);
+ POSTING_READ(PCH_DREF_CONTROL);
+ udelay(200);
+ }
}

BUG_ON(val != final);
--
2.5.5
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