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drm/i915/cnl: Simplify dco_fraction calculation.

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I confess I never fully understood that previous calculation,
so this is not a "fix". But let's simplify this math
so poor brains like mine can read and make some sense of
it in the future.

v2: Don't follow the spec since that gives invalid
    values and it is also confusing. This Ville's
    version is much simpler.
v3: Use u64 cast instead of declaring a u64 dco. (Ville).

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171115184257.8633-1-rodrigo.vivi@intel.com
This commit is contained in:
Rodrigo Vivi 2017-11-15 10:42:57 -08:00
parent cacf6fe7c6
commit 8a00678a09
1 changed files with 6 additions and 3 deletions
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9
drivers/gpu/drm/i915/intel_dpll_mgr.c
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@ -2153,6 +2153,8 @@ static void cnl_wrpll_params_populate(struct skl_wrpll_params *params,
u32 dco_freq, u32 ref_freq,
int pdiv, int qdiv, int kdiv)
{
u32 dco;
switch (kdiv) {
case 1:
params->kdiv = 1;
@ -2189,9 +2191,10 @@ static void cnl_wrpll_params_populate(struct skl_wrpll_params *params,
params->qdiv_ratio = qdiv;
params->qdiv_mode = (qdiv == 1) ? 0 : 1;
params->dco_integer = div_u64(dco_freq, ref_freq);
params->dco_fraction = div_u64((div_u64((uint64_t)dco_freq<<15, (uint64_t)ref_freq) -
((uint64_t)params->dco_integer<<15)) * 0x8000, 0x8000);
dco = div_u64((u64)dco_freq << 15, ref_freq);
params->dco_integer = dco >> 15;
params->dco_fraction = dco & 0x7fff;
}
static bool