[Intel-gfx] [PATCH 2/2] drm/i915: Ignore long hpds on eDP ports

[Dave Airlie]

On 17 October 2014 03:46,  <ville.syrjala at linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> Turning vdd on/off can generate a long hpd pulse on eDP ports. In order
> to handle hpd we would need to turn on vdd to perform aux transfers.
> This would lead to an endless cycle of
> "vdd off -> long hpd -> vdd on -> detect -> vdd off -> ..."
>
> So ignore long hpd pulses on eDP ports. eDP panels should be physically
> tied to the machine anyway so they should not actually disappear and
> thus don't need long hpd handling. Short hpds are still needed for link
> re-train and whatnot so we can't just turn off the hpd interrupt
> entirely for eDP ports. Perhaps we could turn it off whenever the panel
> is disabled, but just ignoring the long hpd seems sufficient.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Hell yes,

I think nouveau just disables the whole irq when they know the outputs
isn't being used,

but this looks good to me.

Reviewed-by: Dave Airlie <airlied at redhat.com>

> ---
>  drivers/gpu/drm/i915/intel_dp.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index f07f02c..4455009 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4611,6 +4611,18 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
>         if (intel_dig_port->base.type != INTEL_OUTPUT_EDP)
>                 intel_dig_port->base.type = INTEL_OUTPUT_DISPLAYPORT;
>
> +       if (long_hpd && intel_dig_port->base.type == INTEL_OUTPUT_EDP) {
> +               /*
> +                * vdd off can generate a long pulse on eDP which
> +                * would require vdd on to handle it, and thus we
> +                * would end up in an endless cycle of
> +                * "vdd off -> long hpd -> vdd on -> detect -> vdd off -> ..."
> +                */
> +               DRM_DEBUG_KMS("ignoring long hpd on eDP port %c\n",
> +                             port_name(intel_dig_port->port));
> +               return false;
> +       }
> +
>         DRM_DEBUG_KMS("got hpd irq on port %c - %s\n",
>                       port_name(intel_dig_port->port),
>                       long_hpd ? "long" : "short");
> --
> 2.0.4
>
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