The audio chicken bit (register offset 0x62f38) seems required to make
DP audio working on some machines. At least, on Dell Wyse 3040, I
failed to get the audio unless this bit is set once.
Strangely, the bit seems necessary only once, and it persists after
that, even some power-off cycles. The register is supposedly
write-only, so it's no evidence whether the bit keeps effect
persistently. But, judging from the experiment, it looks enough to
set it up once at the device initialization.
The patch is basically a cut from the original patch by Pierre-Louis
Bossart.
Cc: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
drivers/gpu/drm/i915/i915_reg.h | 3 +++
drivers/gpu/drm/i915/intel_lpe_audio.c | 7 +++++++
2 files changed, 10 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 4e24ba0cdbe8..4f15a3dc6d98 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -2062,6 +2062,9 @@ enum skl_disp_power_wells {
#define I915_HDMI_LPE_AUDIO_SIZE 0x1000
/* DisplayPort Audio w/ LPE */
+#define VLV_AUD_CHICKEN_BIT_REG _MMIO(VLV_DISPLAY_BASE + 0x62F38)
+#define VLV_CHICKEN_BIT_DBG_ENABLE (1 << 0)
+
#define _VLV_AUD_PORT_EN_B_DBG (VLV_DISPLAY_BASE + 0x62F20)
#define _VLV_AUD_PORT_EN_C_DBG (VLV_DISPLAY_BASE + 0x62F30)
#define _VLV_AUD_PORT_EN_D_DBG (VLV_DISPLAY_BASE + 0x62F34)
diff --git a/drivers/gpu/drm/i915/intel_lpe_audio.c b/drivers/gpu/drm/i915/intel_lpe_audio.c
index d3ffe0012692..3ba2799e93bd 100644
--- a/drivers/gpu/drm/i915/intel_lpe_audio.c
+++ b/drivers/gpu/drm/i915/intel_lpe_audio.c
@@ -248,6 +248,13 @@ static int lpe_audio_setup(struct drm_i915_private *dev_priv)
goto err_free_irq;
}
+ /* enable chicken bit; at least this is required for Dell Wyse 3040
+ * with DP outputs (but only sometimes by some reason!)
+ */
+ I915_WRITE(VLV_AUD_CHICKEN_BIT_REG,
+ I915_READ(VLV_AUD_CHICKEN_BIT_REG) |
+ VLV_CHICKEN_BIT_DBG_ENABLE);
+
return 0;
err_free_irq:
irq_free_desc(dev_priv->lpe_audio.irq);
--
2.11.0
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