[Intel-gfx] [PATCH 2/4] drm/i915/lspcon: Fix resume time initialization due to unasserted HPD

[Imre Deak]

On Sat, Jan 28, 2017 at 10:32:03AM +0530, Sharma, Shashank wrote:
> Regards
> 
> Shashank
> 
> 
> On 1/27/2017 3:09 PM, Imre Deak wrote:
> >During system resume time initialization the HPD level on LSPCON ports
> >can stay low for an extended amount of time, leading to failed AUX
> >transfers and LSPCON initialization. Fix this by waiting for HPD to get
> >asserted.
> >
> >Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99178
> >Cc: Shashank Sharma <shashank.sharma at intel.com>
> >Cc: Jani Nikula <jani.nikula at linux.intel.com>
> >Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> >Cc: <stable at vger.kernel.org> # v4.9+
> >Signed-off-by: Imre Deak <imre.deak at intel.com>
> >---
> >  drivers/gpu/drm/i915/intel_dp.c     | 4 ++--
> >  drivers/gpu/drm/i915/intel_drv.h    | 2 ++
> >  drivers/gpu/drm/i915/intel_lspcon.c | 5 ++++-
> >  3 files changed, 8 insertions(+), 3 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> >index e0f9b9e..a7785ce 100644
> >--- a/drivers/gpu/drm/i915/intel_dp.c
> >+++ b/drivers/gpu/drm/i915/intel_dp.c
> >@@ -4400,8 +4400,8 @@ static bool bxt_digital_port_connected(struct drm_i915_private *dev_priv,
> >   *
> >   * Return %true if @port is connected, %false otherwise.
> >   */
> >-static bool intel_digital_port_connected(struct drm_i915_private *dev_priv,
> >-					 struct intel_digital_port *port)
> >+bool intel_digital_port_connected(struct drm_i915_private *dev_priv,
> >+				  struct intel_digital_port *port)
> >  {
> >  	if (HAS_PCH_IBX(dev_priv))
> >  		return ibx_digital_port_connected(dev_priv, port);
> >diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> >index b71fece..b9cde11 100644
> >--- a/drivers/gpu/drm/i915/intel_drv.h
> >+++ b/drivers/gpu/drm/i915/intel_drv.h
> >@@ -1489,6 +1489,8 @@ bool __intel_dp_read_desc(struct intel_dp *intel_dp,
> >  bool intel_dp_read_desc(struct intel_dp *intel_dp);
> >  int intel_dp_link_required(int pixel_clock, int bpp);
> >  int intel_dp_max_data_rate(int max_link_clock, int max_lanes);
> >+bool intel_digital_port_connected(struct drm_i915_private *dev_priv,
> >+				  struct intel_digital_port *port);
> >  /* intel_dp_aux_backlight.c */
> >  int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector);
> >diff --git a/drivers/gpu/drm/i915/intel_lspcon.c b/drivers/gpu/drm/i915/intel_lspcon.c
> >index f6d4e69..c300647 100644
> >--- a/drivers/gpu/drm/i915/intel_lspcon.c
> >+++ b/drivers/gpu/drm/i915/intel_lspcon.c
> >@@ -158,6 +158,8 @@ static bool lspcon_probe(struct intel_lspcon *lspcon)
> >  static void lspcon_resume_in_pcon_wa(struct intel_lspcon *lspcon)
> >  {
> >  	struct intel_dp *intel_dp = lspcon_to_intel_dp(lspcon);
> >+	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> >+	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
> >  	unsigned long start = jiffies;
> >  	if (!lspcon->desc_valid)
> >@@ -173,7 +175,8 @@ static void lspcon_resume_in_pcon_wa(struct intel_lspcon *lspcon)
> >  		if (!__intel_dp_read_desc(intel_dp, &desc))
> >  			return;
> >-		if (!memcmp(&intel_dp->desc, &desc, sizeof(desc))) {
> >+		if (intel_digital_port_connected(dev_priv, dig_port) &&
> when in PCON mode, live_status is always up for LSPCON port, so this check
> will be always true, isn't it ?

Not at least in case of the MegaChips LSPCON I've seen, there it takes a
while for HPD to get asserted. And while it's not asserted AUX
transactions will either:
- return garbage in case of native AUX transactions
- hang the chip/FW until next cold reboot in case of I2C-over-AUX
  transactions
- simply not get a reply if the chip/FW initialization has reached a
  certain phase

Based on the DP specification the sink/branch device is not required to
respond in case the HPD is not asserted, so the 3rd scenario is
compliant, but the first two are not.

In PCON mode after initialization and HPD getting asserted, HPD will
stay asserted except for the short pulses signaling an output
connect/disconnect.

--Imre

> - Shashank
> >+		    !memcmp(&intel_dp->desc, &desc, sizeof(desc))) {
> >  			DRM_DEBUG_KMS("LSPCON recovering in PCON mode after %u ms\n",
> >  				      jiffies_to_msecs(jiffies - start));
> >  			return;
>