Re: [Intel-gfx] [PATCH 07/11] drm/i915: Store the m2 divider as a whole in bxt_clk_div

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Mar 04, 2022 at 01:36:27PM +0200, Jani Nikula wrote:
> On Tue, 01 Mar 2022, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Get rid of the pointless m2 int vs. frac split in bxt_clk_div
> > and just store the whole divider as one.
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dpll_mgr.c | 33 +++++++++++--------
> >  1 file changed, 19 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> > index 899aa42a858f..4a82e630cbec 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> > @@ -2085,8 +2085,7 @@ struct bxt_clk_div {
> >  	int clock;
> >  	u32 p1;
> >  	u32 p2;
> > -	u32 m2_int;
> > -	u32 m2_frac;
> > +	u32 m2;
> >  	u32 n;
> >  
> >  	int vco;
> > @@ -2094,13 +2093,20 @@ struct bxt_clk_div {
> >  
> >  /* pre-calculated values for DP linkrates */
> >  static const struct bxt_clk_div bxt_dp_clk_val[] = {
> > -	{ .clock = 162000, .p1 = 4, .p2 = 2, .m2_int = 32, .m2_frac = 1677722, .n = 1, },
> > -	{ .clock = 270000, .p1 = 4, .p2 = 1, .m2_int = 27, .m2_frac =       0, .n = 1, },
> > -	{ .clock = 540000, .p1 = 2, .p2 = 1, .m2_int = 27, .m2_frac =       0, .n = 1, },
> > -	{ .clock = 216000, .p1 = 3, .p2 = 2, .m2_int = 32, .m2_frac = 1677722, .n = 1, },
> > -	{ .clock = 243000, .p1 = 4, .p2 = 1, .m2_int = 24, .m2_frac = 1258291, .n = 1, },
> > -	{ .clock = 324000, .p1 = 4, .p2 = 1, .m2_int = 32, .m2_frac = 1677722, .n = 1, },
> > -	{ .clock = 432000, .p1 = 3, .p2 = 1, .m2_int = 32, .m2_frac = 1677722, .n = 1, },
> > +	{ .clock = 162000, .p1 = 4, .p2 = 2, .n = 1,
> > +	  .m2 = 0x819999a /* .m2_int = 32, m2_frac = 1677722 */ },
> > +	{ .clock = 270000, .p1 = 4, .p2 = 1, .n = 1,
> > +	  .m2 = 0x6c00000 /* .m2_int = 27, m2_frac =       0 */ },
> > +	{ .clock = 540000, .p1 = 2, .p2 = 1, .n = 1,
> > +	  .m2 = 0x6c00000 /* .m2_int = 27, m2_frac =       0 */ },
> > +	{ .clock = 216000, .p1 = 3, .p2 = 2, .n = 1,
> > +	  .m2 = 0x819999a /* .m2_int = 32, m2_frac = 1677722 */ },
> > +	{ .clock = 243000, .p1 = 4, .p2 = 1, .n = 1,
> > +	  .m2 = 0x6133333 /* .m2_int = 24, m2_frac = 1258291 */ },
> > +	{ .clock = 324000, .p1 = 4, .p2 = 1, .n = 1,
> > +	  .m2 = 0x819999a /* .m2_int = 32, m2_frac = 1677722 */ },
> > +	{ .clock = 432000, .p1 = 3, .p2 = 1, .n = 1,
> > +	  .m2 = 0x819999a /* .m2_int = 32, m2_frac = 1677722 */ },
> 
> Mmh, I guess here I would've added some macros to construct m2 from
> m2_int and m2_frac.
> 
> #define M2_INT_SHIFT	22
> #define M2_FRAC_MASK	0x3fffff
> 
> #define M2(int, frac) ((int) << M2_INT_SHIFT) | (frac))

I don't think this weird decimal representation of m2 is useful
for anything actually. I just copy-pasted it from the chv side
for consistency. Should just probably nuke it for both.

I guess the sensible thing would be to just write the full m2 in
decimal in the comment, eg. ".m2 = 0x819999a /* 32.4 */"

Hmm. Or we could even go a bit further and just do:
.m2 = 32.4 * (1 << 22) + .5
and hope the compiler evaluates it at compile time instead
of getting upset about the floats.

> 
> And you get this:
> 
> 	{ .clock = 432000, .p1 = 3, .p2 = 1, .m2 = M2(32, 1677722), .n = 1, },
> 
> No need to retain the int/frac in comments. Can also use
> REG_FIELD_PREP/GET if you want to over-engineer...
> 
> >  };
> >  
> >  static bool
> > @@ -2127,8 +2133,7 @@ bxt_ddi_hdmi_pll_dividers(struct intel_crtc_state *crtc_state,
> >  	clk_div->p2 = best_clock.p2;
> >  	drm_WARN_ON(&i915->drm, best_clock.m1 != 2);
> >  	clk_div->n = best_clock.n;
> > -	clk_div->m2_int = best_clock.m2 >> 22;
> > -	clk_div->m2_frac = best_clock.m2 & ((1 << 22) - 1);
> > +	clk_div->m2 = best_clock.m2;
> >  
> >  	clk_div->vco = best_clock.vco;
> >  
> > @@ -2197,11 +2202,11 @@ static bool bxt_ddi_set_dpll_hw_state(struct intel_crtc_state *crtc_state,
> >  		lanestagger = 0x02;
> >  
> >  	dpll_hw_state->ebb0 = PORT_PLL_P1(clk_div->p1) | PORT_PLL_P2(clk_div->p2);
> > -	dpll_hw_state->pll0 = clk_div->m2_int;
> > +	dpll_hw_state->pll0 = clk_div->m2 >> 22;
> >  	dpll_hw_state->pll1 = PORT_PLL_N(clk_div->n);
> > -	dpll_hw_state->pll2 = clk_div->m2_frac;
> > +	dpll_hw_state->pll2 = clk_div->m2 & 0x3fffff;

I should probably use the REG_FIELD_PREP() macros consistently here.

> >  
> > -	if (clk_div->m2_frac)
> > +	if (clk_div->m2 & 0x3fffff)
> >  		dpll_hw_state->pll3 = PORT_PLL_M2_FRAC_ENABLE;

But here such usage would imply tht the reg value == m2
fractional part. That does happen to be the case here but 
not sure I want to write the code in a way that assumes that.

> 
> Also could reuse the shift and mask macros here.
> 
> Other than that, the direction seems good.
> 
> BR,
> Jani.
> 
> 
> >  
> >  	dpll_hw_state->pll6 = prop_coef | PORT_PLL_INT_COEFF(int_coef);
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Ville Syrjälä
Intel