[Intel-gfx] [PATCH 1/5] drm/i915/skl: Work around incorrect BIOS WRPLL PDIV programming

[Ville Syrjälä]

On Sat, Oct 03, 2020 at 03:18:42AM +0300, Imre Deak wrote:
> The BIOS of at least one ASUS-Z170M system with an SKL I have programs
> the 101b WRPLL PDIV divider value, which is the encoding for PDIV=7 with
> bit#0 incorrectly set.
> 
> This happens with the
> 
> "3840x2160": 30 262750 3840 3888 3920 4000 2160 2163 2168 2191 0x48 0x9
> 
> HDMI mode (scaled from a 1024x768 src fb) set by BIOS and the
> 
> ref_clock=24000, dco_integer=383, dco_fraction=5802, pdiv=7, qdiv=1, kdiv=1
> 
> WRPLL parameters (assuming PDIV=7 was the intended setting). This
> corresponds to 262749 PLL frequency/port clock.
> 
> Later the driver sets the same mode for which it calculates the same
> dco_int/dco_frac/div WRPLL parameters (with the correct PDIV=7 encoding).
> 
> Based on the above, let's assume that PDIV=7 was intended and the HW
> just ignores bit#0 in the PDIV register field for this setting, treating
> 100b and 101b encodings the same way.
> 
> While at it add the MISSING_CASE() for the p0,p2 divider decodings.
> 
> v2: (Ville)
> - Add a define for the incorrect divider value.
> - Emit only a debug message when detecting the incorrect divider value.
> - Use fallthrough from the incorrect divider value case.
> - Add the MISSING_CASE()s.
> 
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dpll_mgr.c | 14 ++++++++++++++
>  drivers/gpu/drm/i915/i915_reg.h               |  1 +
>  2 files changed, 15 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> index e08684e34078..61cb558c60d1 100644
> --- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> +++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> @@ -1602,12 +1602,26 @@ static int skl_ddi_wrpll_get_freq(struct drm_i915_private *i915,
>  	case DPLL_CFGCR2_PDIV_3:
>  		p0 = 3;
>  		break;
> +	default:
> +		if (p0 == DPLL_CFGCR2_PDIV_7_INVALID)

Why not just 'case DPLL_CFGCR2_PDIV_7_INVALID:' ?

> +			/*
> +			 * Incorrect ASUS-Z170M BIOS setting, the HW seems to ignore bit#0,
> +			 * handling it the same way as PDIV_7.
> +			 */
> +			drm_dbg_kms(&i915->drm, "Invalid WRPLL PDIV divider value, fixing it.\n");
> +		else
> +			MISSING_CASE(p0);
> +
> +		fallthrough;
>  	case DPLL_CFGCR2_PDIV_7:
>  		p0 = 7;
>  		break;
>  	}
>  
>  	switch (p2) {
> +	default:
> +		MISSING_CASE(p2);
> +		fallthrough;

Is there a specific reason we fall through to the 5 and 7 cases for
bogus values?

>  	case DPLL_CFGCR2_KDIV_5:
>  		p2 = 5;
>  		break;
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 88c215cf97d4..d911583526db 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -10261,6 +10261,7 @@ enum skl_power_gate {
>  #define  DPLL_CFGCR2_PDIV_2 (1 << 2)
>  #define  DPLL_CFGCR2_PDIV_3 (2 << 2)
>  #define  DPLL_CFGCR2_PDIV_7 (4 << 2)
> +#define  DPLL_CFGCR2_PDIV_7_INVALID	(5 << 2)
>  #define  DPLL_CFGCR2_CENTRAL_FREQ_MASK	(3)
>  
>  #define DPLL_CFGCR1(id)	_MMIO_PIPE((id) - SKL_DPLL1, _DPLL1_CFGCR1, _DPLL2_CFGCR1)
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel