[PATCH] Revert "drm/i915/dp: Use auxch precharge value of 5 everywhere"

[PATCH] Revert "drm/i915/dp: Use auxch precharge value of 5 everywhere"

[Daniel Vetter]

This reverts commit 092945e11c5b84f66dd08f0b87fb729715d377bc.

This commit prevents a DP screen from properly training the link.
Oddly enough it works, once the machine has been warm-boot with an
older kernel.

According to DP docs this _should_ have been the right precharge time.
Also, the commit that originally introduce this was just general snb
DP enabling and didn't mention any specific reason for this special
value. Whatever, trust the reporter that this makes things worse.

Cc: Adam Jackson <ajax@redhat.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Reported-by: "Wouter M. Koolen" <W.M.Koolen-Wijkstra@cwi.nl>
Buglink: https://lkml.org/lkml/2012/6/14/301
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_dp.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index c574ff0..a4b3887 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -371,7 +371,7 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 	int recv_bytes;
 	uint32_t status;
 	uint32_t aux_clock_divider;
-	int try, precharge = 5;
+	int try, precharge;
 
 	intel_dp_check_edp(intel_dp);
 	/* The clock divider is based off the hrawclk,
@@ -391,6 +391,11 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 	else
 		aux_clock_divider = intel_hrawclk(dev) / 2;
 
+	if (IS_GEN6(dev))
+		precharge = 3;
+	else
+		precharge = 5;
+
 	/* Try to wait for any previous AUX channel activity */
 	for (try = 0; try < 3; try++) {
 		status = I915_READ(ch_ctl);
-- 
1.7.10

[PATCH] Revert "drm/i915/dp: Use auxch precharge value of 5 everywhere"

[Daniel Vetter]

This reverts commit 092945e11c5b84f66dd08f0b87fb729715d377bc.

This commit prevents a DP screen from properly training the link.
Oddly enough it works, once the machine has been warm-booted with an
older kernel.

According to DP docs this _should_ have been the right precharge time.
Also, the commit that originally introduces this was just general snb
DP enabling and didn't mention any specific reason for this special
value. Whatever, trust the reporter that this makes things worse and
let's just revert it.

v2: Less spelling fail.

Cc: Adam Jackson <ajax@redhat.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Reported-by: "Wouter M. Koolen" <W.M.Koolen-Wijkstra@cwi.nl>
Buglink: https://lkml.org/lkml/2012/6/14/301
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_dp.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index c574ff0..a4b3887 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -371,7 +371,7 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 	int recv_bytes;
 	uint32_t status;
 	uint32_t aux_clock_divider;
-	int try, precharge = 5;
+	int try, precharge;
 
 	intel_dp_check_edp(intel_dp);
 	/* The clock divider is based off the hrawclk,
@@ -391,6 +391,11 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 	else
 		aux_clock_divider = intel_hrawclk(dev) / 2;
 
+	if (IS_GEN6(dev))
+		precharge = 3;
+	else
+		precharge = 5;
+
 	/* Try to wait for any previous AUX channel activity */
 	for (try = 0; try < 3; try++) {
 		status = I915_READ(ch_ctl);
-- 
1.7.10

Re: [PATCH] Revert "drm/i915/dp: Use auxch precharge value of 5 everywhere"

[Daniel Vetter]

On Thu, Jun 14, 2012 at 10:15:00PM +0200, Daniel Vetter wrote:
> This reverts commit 092945e11c5b84f66dd08f0b87fb729715d377bc.
> 
> This commit prevents a DP screen from properly training the link.
> Oddly enough it works, once the machine has been warm-booted with an
> older kernel.
> 
> According to DP docs this _should_ have been the right precharge time.
> Also, the commit that originally introduces this was just general snb
> DP enabling and didn't mention any specific reason for this special
> value. Whatever, trust the reporter that this makes things worse and
> let's just revert it.
> 
> v2: Less spelling fail.
> 
> Cc: Adam Jackson <ajax@redhat.com>
> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> Reported-by: "Wouter M. Koolen" <W.M.Koolen-Wijkstra@cwi.nl>
> Buglink: https://lkml.org/lkml/2012/6/14/301
> Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
No one yelled around with a better idea, so I've picked this up for fixes
with cc stable.
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48