On Tue, Dec 27, 2016 at 06:59:54PM +0530, Animesh Manna wrote:
> _DSM is added to program HPD_CTL(0x1094) register
> of PMC from i915 driver which will be called
> based on driver feature flag.
> 
> During S0ix display engine is completely powered down. Hot plug will be
> missed by display HPD detection logic. GPIO unit detect any edge on HPD
> pin and then triggers PMC->Punit to power up and restore display.
> By programming PMC hpd control register we are enabling the manual
> trigger from Punit which will be done by writing the PM interrupt register.
> 
> Note: Display engine continue to get HPD interrupt even after DC9 but
> the system is in S0 state (VNN will be on).
> 
> v1: Initial version as RFC.
> 
> v2: Modified the commit message.
> 
> Signed-off-by: Animesh Manna <[email protected]>
> ---
>  drivers/gpu/drm/i915/intel_acpi.c | 32 +++++++++++++++++++++++++++-----
>  1 file changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_acpi.c 
> b/drivers/gpu/drm/i915/intel_acpi.c
> index 5c49cef..47b8bbd 100644
> --- a/drivers/gpu/drm/i915/intel_acpi.c
> +++ b/drivers/gpu/drm/i915/intel_acpi.c
> @@ -10,6 +10,8 @@
>  
>  #define INTEL_DSM_REVISION_ID 1 /* For Calpella anyway... */
>  #define INTEL_DSM_FN_PLATFORM_MUX_INFO 1 /* No args */
> +#define INTEL_DSM_SET_HPD_WAKEUP 17
> +#define HPD_WAKEUP_EN_VAL 0xFCF0
>  
>  static struct intel_dsm_priv {
>       acpi_handle dhandle;
> @@ -118,6 +120,25 @@ static void intel_dsm_platform_mux_info(void)
>       ACPI_FREE(pkg);
>  }
>  
> +static void intel_dsm_set_hpd_wakeup(const u8 *guid)
> +{
> +     union acpi_object *obj;
> +     union acpi_object argv4 = {
> +             .integer.type = ACPI_TYPE_INTEGER,
> +             .integer.value = HPD_WAKEUP_EN_VAL,
> +     };
> +
> +     obj = acpi_evaluate_dsm_typed(intel_dsm_priv.dhandle, guid,
> +                     INTEL_DSM_REVISION_ID, INTEL_DSM_SET_HPD_WAKEUP,
> +                     &argv4, ACPI_TYPE_INTEGER);

Did this call succeed for you? For me on all platforms I tried
it results in
ACPI Warning: \_SB.PCI0.GFX0._DSM: Argument #4 type mismatch - Found [Integer], 
ACPI requires [Package] (20160930/nsarguments-95)
and the above function returning NULL.

> +
> +     if (!obj)
> +             DRM_DEBUG_DRIVER("failed to evaluate _DSM\n");
> +
> +     ACPI_FREE(obj);
> +}
> +
> +
>  static bool intel_dsm_pci_probe(struct pci_dev *pdev)
>  {
>       acpi_handle dhandle;
> @@ -131,11 +152,12 @@ static bool intel_dsm_pci_probe(struct pci_dev *pdev)
>       intel_dsm_priv.dhandle = dhandle;
>  
>       if (IS_BROXTON(dev_priv)) {
> -             union acpi_object *obj;
> -
> -             obj = acpi_evaluate_dsm(dhandle, intel_dsm_guid_bxt,
> -                                     INTEL_DSM_REVISION_ID, 0, NULL);
> -             if (!obj)
> +             if (dev_priv->vbt.hpd_wakeup_enabled &&
> +                 acpi_check_dsm(dhandle, intel_dsm_guid_bxt,
> +                                INTEL_DSM_REVISION_ID,
> +                                1 << INTEL_DSM_SET_HPD_WAKEUP))
> +                     intel_dsm_set_hpd_wakeup(intel_dsm_guid_bxt);
> +             else
>                       return false;
>       } else {
>               if (acpi_check_dsm(dhandle, intel_dsm_guid,
> -- 
> 2.7.4
> 
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