It should be programmed to "0" for HDMI or "1" for DisplayPort. This enables DisplayPort audio for - HP EliteBook 8460p (whose BIOS does not set the N_value_index bit for us) - DisplayPort monitor hot plugged after boot (otherwise most BIOS will fill the N_value_index bit for us) Signed-off-by: Wu Fengguang <fengguang.wu at intel.com> --- drivers/gpu/drm/i915/i915_reg.h | 3 +++ drivers/gpu/drm/i915/intel_display.c | 5 +++++ 2 files changed, 8 insertions(+) --- linux.orig/drivers/gpu/drm/i915/i915_reg.h 2012-01-06 15:00:55.000000000 +0800 +++ linux/drivers/gpu/drm/i915/i915_reg.h 2012-01-06 15:04:10.000000000 +0800 @@ -3582,4 +3582,7 @@ #define CPT_AUD_CNTL_ST_A 0xE50B4 #define CPT_AUD_CNTRL_ST2 0xE50C0 +#define IBX_AUD_CONFIG_A 0xe2000 +#define CPT_AUD_CONFIG_A 0xe5000 + #endif /* _I915_REG_H_ */ --- linux.orig/drivers/gpu/drm/i915/intel_display.c 2012-01-06 15:05:47.000000000 +0800 +++ linux/drivers/gpu/drm/i915/intel_display.c 2012-01-06 16:07:59.000000000 +0800 @@ -5908,15 +5908,18 @@ static void ironlake_write_eld(struct dr uint32_t i; int len; int hdmiw_hdmiedid; + int aud_config; int aud_cntl_st; int aud_cntrl_st2; if (HAS_PCH_IBX(connector->dev)) { hdmiw_hdmiedid = IBX_HDMIW_HDMIEDID_A; + aud_config = IBX_AUD_CONFIG_A; aud_cntl_st = IBX_AUD_CNTL_ST_A; aud_cntrl_st2 = IBX_AUD_CNTL_ST2; } else { hdmiw_hdmiedid = CPT_HDMIW_HDMIEDID_A; + aud_config = CPT_AUD_CONFIG_A; aud_cntl_st = CPT_AUD_CNTL_ST_A; aud_cntrl_st2 = CPT_AUD_CNTRL_ST2; } @@ -5924,6 +5927,7 @@ static void ironlake_write_eld(struct dr i = to_intel_crtc(crtc)->pipe; hdmiw_hdmiedid += i * 0x100; aud_cntl_st += i * 0x100; + aud_config += i * 0x100; DRM_DEBUG_DRIVER("ELD on pipe %c\n", pipe_name(i)); @@ -5943,6 +5947,7 @@ static void ironlake_write_eld(struct dr if (intel_pipe_has_type(crtc, INTEL_OUTPUT_DISPLAYPORT)) { DRM_DEBUG_DRIVER("ELD: DisplayPort detected\n"); eld[5] |= (1 << 2); /* Conn_Type, 0x1 = DisplayPort */ + I915_WRITE(aud_config, 1 << 29); /* N value index, 0x1 = DP */ } if (intel_eld_uptodate(connector,