[PATCH v2 3/3] drm/i915/pch: abstract fake PCH detection better

[Borah, Chaitanya Kumar]

> -----Original Message-----
> From: Intel-xe <intel-xe-bounces at lists.freedesktop.org> On Behalf Of Jani
> Nikula
> Sent: Thursday, April 17, 2025 2:41 PM
> To: intel-gfx at lists.freedesktop.org; intel-xe at lists.freedesktop.org
> Cc: Nikula, Jani <jani.nikula at intel.com>
> Subject: [PATCH v2 3/3] drm/i915/pch: abstract fake PCH detection better
> 
> Abstract detection of platforms with south display on the same PCI device or
> SoC die as north display, and all around clarify what this means. Debug log
> about it for good measure.
> 
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>

LGTM

Reviewed-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_pch.c | 47 ++++++++++++++----------
>  1 file changed, 28 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_pch.c
> b/drivers/gpu/drm/i915/display/intel_pch.c
> index fec1919e5386..5035b63a4889 100644
> --- a/drivers/gpu/drm/i915/display/intel_pch.c
> +++ b/drivers/gpu/drm/i915/display/intel_pch.c
> @@ -39,6 +39,28 @@
>  #define INTEL_PCH_P3X_DEVICE_ID_TYPE		0x7000
>  #define INTEL_PCH_QEMU_DEVICE_ID_TYPE		0x2900 /* qemu q35
> has 2918 */
> 
> +/*
> + * Check for platforms where the south display is on the same PCI
> +device or SoC
> + * die as the north display. The PCH (if it even exists) is not
> +involved in
> + * display. Return a fake PCH type for south display handling on these
> + * platforms, without actually detecting the PCH, and PCH_NONE otherwise.
> + */
> +static enum intel_pch intel_pch_fake_for_south_display(struct
> +intel_display *display) {
> +	enum intel_pch pch_type = PCH_NONE;
> +
> +	if (DISPLAY_VER(display) >= 20)
> +		pch_type = PCH_LNL;
> +	else if (display->platform.battlemage || display->platform.meteorlake)
> +		pch_type = PCH_MTL;
> +	else if (display->platform.dg2)
> +		pch_type = PCH_DG2;
> +	else if (display->platform.dg1)
> +		pch_type = PCH_DG1;
> +
> +	return pch_type;
> +}
> +
>  /* Map PCH device id to PCH type, or PCH_NONE if unknown. */  static enum
> intel_pch  intel_pch_type(const struct intel_display *display, unsigned short
> id) @@ -258,25 +280,12 @@ void intel_pch_detect(struct intel_display
> *display)
>  	unsigned short id;
>  	enum intel_pch pch_type;
> 
> -	/*
> -	 * South display engine on the same PCI device: just assign the fake
> -	 * PCH.
> -	 */
> -	if (DISPLAY_VER(display) >= 20) {
> -		display->pch_type = PCH_LNL;
> -		return;
> -	} else if (display->platform.battlemage || display-
> >platform.meteorlake) {
> -		/*
> -		 * Both north display and south display are on the SoC die.
> -		 * The real PCH (if it even exists) is uninvolved in display.
> -		 */
> -		display->pch_type = PCH_MTL;
> -		return;
> -	} else if (display->platform.dg2) {
> -		display->pch_type = PCH_DG2;
> -		return;
> -	} else if (display->platform.dg1) {
> -		display->pch_type = PCH_DG1;
> +	pch_type = intel_pch_fake_for_south_display(display);
> +	if (pch_type != PCH_NONE) {
> +		display->pch_type = pch_type;
> +		drm_dbg_kms(display->drm,
> +			    "PCH not involved in display, using fake PCH type %d
> for south display\n",
> +			    pch_type);
>  		return;
>  	}
> 
> --
> 2.39.5