[Intel-gfx] [PATCH v3 7/9] drm/i915/tgl: Fix dkl link training

[Souza, Jose]

On Tue, 2019-09-24 at 18:58 +0300, Imre Deak wrote:
> On Mon, Sep 23, 2019 at 12:55:11PM -0700, José Roberto de Souza
> wrote:
> > Link training is failling when running link at 2.7GHz and 1.62GHz
> > and
> > following BSpec pll algorithm.
> > 
> > Comparing the values calculated and the ones from the reference
> > table
> > it looks like MG_CLKTOP2_CORECLKCTL1_A_DIVRATIO should not always
> > set
> > to 5. For DP ports ICL mg pll algorithm sets it to 10 or 5 based on
> > div2 value, that matches with dkl hardcoded table.
> > 
> > So implementing this way as it proved to work in HW and leaving a
> > comment so we know why it do not match BSpec.
> > 
> > Issue reported on BSpec 49204.
> > 
> > Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dpll_mgr.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> > b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> > index 496df4095a21..3c881d4cf973 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
> > @@ -2631,7 +2631,12 @@ static bool icl_mg_pll_find_divisors(int
> > clock_khz, bool is_dp, bool use_ssc,
> >  
> >  			if (div2 >= 2) {
> >  				if (is_dkl) {
> > -					a_divratio = 5;
> > +					/*
> > +					 * Note: a_divratio not
> > matching TGL
> > +					 * BSpec algorithm but matching
> > +					 * hardcoded values and working
> > on HW
> > +					 */
> > +					a_divratio = 10;
> 
> Yes, matches the hardcoded values for CLKTOP2_HSCLKCTL/CORECLKCTL1,
> with
> the exception that the hardcoded value for CLKTOP2_HSCLKCTL 5p4 is
> also
> incorrect wrt. div2 within that (should be 1 but it's 2).
> 
> However we don't have any hardcoded values in Bspec for HDMI except
> for
> the 5.94Gbps/div2=1 case. So until otherwise proven, for HDMI/div2>=2
> I
> wouldn't change the value, rather have the same logic as for ICL that
> is
> is_dp ? 10 : 5;

I was trying to avoid touch any HDMI calculation as I can't test it but
it looks sane, so I will keep the if is_dkl, replace to "a_divratio =
is_dp ? 10 : 5;" and add to the comment that this is the supposed value
for HDMI but it is not tested.

> 
> >  					tlinedrv = 1;
> >  				} else {
> >  					a_divratio = is_dp ? 10 : 5;
> > -- 
> > 2.23.0
> > 
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