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

[Ville Syrjälä]

On Tue, Sep 29, 2020 at 03:29:25AM +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.
> 
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dpll_mgr.c | 8 ++++++++
>  drivers/gpu/drm/i915/i915_reg.h               | 1 +
>  2 files changed, 9 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..095b53fe3a21 100644
> --- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> +++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> @@ -1602,6 +1602,14 @@ static int skl_ddi_wrpll_get_freq(struct drm_i915_private *i915,
>  	case DPLL_CFGCR2_PDIV_3:
>  		p0 = 3;
>  		break;
> +	case DPLL_CFGCR2_PDIV_7 | (1 << DPLL_CFGCR2_PDIV_SHIFT):

Maybe we want a define for this?

> +		/*
> +		 * Incorrect ASUS-Z170M BIOS setting, the HW seems to ignore bit#0,
> +		 * handling it the same way as PDIV_7.
> +		 */
> +		drm_err(&i915->drm, "Invalid WRPLL PDIV divider value, fixing it.\n");

I wonder how many bug reports that will generate. Might want to make
it debug insteead.

> +		p0 = 7;
> +		break;

Or maybe fallthrough?

>  	case DPLL_CFGCR2_PDIV_7:
>  		p0 = 7;
>  		break;
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 47730a176698..f70e45bd3810 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -10253,6 +10253,7 @@ enum skl_power_gate {
>  #define  DPLL_CFGCR2_KDIV_3 (2 << 5)
>  #define  DPLL_CFGCR2_KDIV_1 (3 << 5)
>  #define  DPLL_CFGCR2_PDIV_MASK		(7 << 2)
> +#define  DPLL_CFGCR2_PDIV_SHIFT		2
>  #define  DPLL_CFGCR2_PDIV(x)		((x) << 2)
>  #define  DPLL_CFGCR2_PDIV_1 (0 << 2)
>  #define  DPLL_CFGCR2_PDIV_2 (1 << 2)
> -- 
> 2.25.1
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel