This is a note to let you know that I've just added the patch titled
drm/i915: Explain the magic numbers for AUX SYNC/precharge length
to the 6.1-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-explain-the-magic-numbers-for-aux-sync-prec.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4ab09dc7a39143679b741de19b145e8cebe3608f
Author: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Date: Wed Mar 29 20:24:34 2023 +0300
drm/i915: Explain the magic numbers for AUX SYNC/precharge length
[ Upstream commit 26bfc3f36f2104c174dfc72415547d5c28ef3f1c ]
Replace the hardcoded final numbers in the AUX SYNC/precharge
setup, and derive those from numbers from the (e)DP specs.
The new functions can serve as the single point of truth for
the number of SYNC pulses we use.
Cc: Jouni Högander <jouni.hogander@xxxxxxxxx>
Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20230329172434.18744-2-ville.syrjala@xxxxxxxxxxxxxxx
Reviewed-by: Jouni Högander <jouni.hogander@xxxxxxxxx>
Stable-dep-of: 2d6f2f79e065 ("drm/i915: Use 18 fast wake AUX sync len")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
index 7f3f2d50e6cde..8325868770994 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
@@ -119,6 +119,32 @@ static u32 skl_get_aux_clock_divider(struct intel_dp *intel_dp, int index)
return index ? 0 : 1;
}
+static int intel_dp_aux_sync_len(void)
+{
+ int precharge = 16; /* 10-16 */
+ int preamble = 16;
+
+ return precharge + preamble;
+}
+
+static int intel_dp_aux_fw_sync_len(void)
+{
+ int precharge = 16; /* 10-16 */
+ int preamble = 8;
+
+ return precharge + preamble;
+}
+
+static int g4x_dp_aux_precharge_len(void)
+{
+ int precharge_min = 10;
+ int preamble = 16;
+
+ /* HW wants the length of the extra precharge in 2us units */
+ return (intel_dp_aux_sync_len() -
+ precharge_min - preamble) / 2;
+}
+
static u32 g4x_get_aux_send_ctl(struct intel_dp *intel_dp,
int send_bytes,
u32 aux_clock_divider)
@@ -141,7 +167,7 @@ static u32 g4x_get_aux_send_ctl(struct intel_dp *intel_dp,
timeout |
DP_AUX_CH_CTL_RECEIVE_ERROR |
(send_bytes << DP_AUX_CH_CTL_MESSAGE_SIZE_SHIFT) |
- (3 << DP_AUX_CH_CTL_PRECHARGE_2US_SHIFT) |
+ (g4x_dp_aux_precharge_len() << DP_AUX_CH_CTL_PRECHARGE_2US_SHIFT) |
(aux_clock_divider << DP_AUX_CH_CTL_BIT_CLOCK_2X_SHIFT);
}
@@ -165,8 +191,8 @@ static u32 skl_get_aux_send_ctl(struct intel_dp *intel_dp,
DP_AUX_CH_CTL_TIME_OUT_MAX |
DP_AUX_CH_CTL_RECEIVE_ERROR |
(send_bytes << DP_AUX_CH_CTL_MESSAGE_SIZE_SHIFT) |
- DP_AUX_CH_CTL_FW_SYNC_PULSE_SKL(24) |
- DP_AUX_CH_CTL_SYNC_PULSE_SKL(32);
+ DP_AUX_CH_CTL_FW_SYNC_PULSE_SKL(intel_dp_aux_fw_sync_len()) |
+ DP_AUX_CH_CTL_SYNC_PULSE_SKL(intel_dp_aux_sync_len());
if (intel_tc_port_in_tbt_alt_mode(dig_port))
ret |= DP_AUX_CH_CTL_TBT_IO;
