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

[Imre Deak]

On Thu, Oct 01, 2020 at 07:41:48PM +0300, Ville Syrjälä wrote:
> 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?

Ok.

> 
> > +		/*
> > +		 * 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.

I thought having reports for this is actually good, since BIOS vendors
should be notified then, but can change this to debug.

> 
> > +		p0 = 7;
> > +		break;
> 
> Or maybe fallthrough?

can do if you have an idea how to do that with the MISSING_CASE() added
later setting pdiv=7 by default.

> 
> >  	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