Re: [PATCH 11/12] drm/i915: Filter out glitches on HPD lines during hotplug detection

["Hogander, Jouni" <jouni.hogander@intel.com>]

On Thu, 2024-01-04 at 10:30 +0200, Imre Deak wrote:
> Glitches deasserting the connector HPD line can lead to incorrectly
> detecting a disconnect event (a glitch asserting the line will only
> cause a redundant connect->disconnect transition). The source of such
> a
> glitch can be noise on the line or a 0.5ms-1ms MST IRQ_HPD pulse.
> TypeC
> ports in the DP-alt or TBT-alt mode filter out these glitches
> inernally,
> but for others the driver has to do this. Make it so by polling the
> HPD
> line on these connectors for 4 ms.
> 
> Signed-off-by: Imre Deak <imre.deak@intel.com>

Reviewed-by: Jouni Högander <jouni.hogander@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 13 +++++++++++--
>  drivers/gpu/drm/i915/display/intel_tc.c |  9 +++++++++
>  drivers/gpu/drm/i915/display/intel_tc.h |  1 +
>  3 files changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index f04926d4aa80d..77ba6de6ba087 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5460,11 +5460,20 @@ bool
> intel_digital_port_connected_locked(struct intel_encoder *encoder)
>  {
>         struct drm_i915_private *dev_priv = to_i915(encoder-
> >base.dev);
>         struct intel_digital_port *dig_port =
> enc_to_dig_port(encoder);
> +       bool is_glitch_free =
> intel_tc_port_handles_hpd_glitches(dig_port);
>         bool is_connected = false;
>         intel_wakeref_t wakeref;
>  
> -       with_intel_display_power(dev_priv, POWER_DOMAIN_DISPLAY_CORE,
> wakeref)
> -               is_connected = dig_port->connected(encoder);
> +       with_intel_display_power(dev_priv, POWER_DOMAIN_DISPLAY_CORE,
> wakeref) {
> +               unsigned long wait_expires = jiffies +
> msecs_to_jiffies_timeout(4);
> +
> +               do {
> +                       is_connected = dig_port->connected(encoder);
> +                       if (is_connected || is_glitch_free)
> +                               break;
> +                       usleep_range(10, 30);
> +               } while (time_before(jiffies, wait_expires));
> +       }
>  
>         return is_connected;
>  }
> diff --git a/drivers/gpu/drm/i915/display/intel_tc.c
> b/drivers/gpu/drm/i915/display/intel_tc.c
> index 80aed9e87927a..f34743e6eeed2 100644
> --- a/drivers/gpu/drm/i915/display/intel_tc.c
> +++ b/drivers/gpu/drm/i915/display/intel_tc.c
> @@ -122,6 +122,15 @@ bool intel_tc_port_in_legacy_mode(struct
> intel_digital_port *dig_port)
>         return intel_tc_port_in_mode(dig_port, TC_PORT_LEGACY);
>  }
>  
> +bool intel_tc_port_handles_hpd_glitches(struct intel_digital_port
> *dig_port)
> +{
> +       struct drm_i915_private *i915 = to_i915(dig_port-
> >base.base.dev);
> +       enum phy phy = intel_port_to_phy(i915, dig_port->base.port);
> +       struct intel_tc_port *tc = to_tc_port(dig_port);
> +
> +       return intel_phy_is_tc(i915, phy) && !tc->legacy_port;
> +}
> +
>  /*
>   * The display power domains used for TC ports depending on the
>   * platform and TC mode (legacy, DP-alt, TBT):
> diff --git a/drivers/gpu/drm/i915/display/intel_tc.h
> b/drivers/gpu/drm/i915/display/intel_tc.h
> index 936fa2daaa74a..26c4265368c1a 100644
> --- a/drivers/gpu/drm/i915/display/intel_tc.h
> +++ b/drivers/gpu/drm/i915/display/intel_tc.h
> @@ -15,6 +15,7 @@ struct intel_encoder;
>  bool intel_tc_port_in_tbt_alt_mode(struct intel_digital_port
> *dig_port);
>  bool intel_tc_port_in_dp_alt_mode(struct intel_digital_port
> *dig_port);
>  bool intel_tc_port_in_legacy_mode(struct intel_digital_port
> *dig_port);
> +bool intel_tc_port_handles_hpd_glitches(struct intel_digital_port
> *dig_port);
>  
>  bool intel_tc_port_connected(struct intel_encoder *encoder);
>