From 8a00678a096445716861d2c0bd2a7007ad373f4d Mon Sep 17 00:00:00 2001
From: Rodrigo Vivi <rodrigo.vivi@intel.com>
Date: Wed, 15 Nov 2017 10:42:57 -0800
Subject: [PATCH] drm/i915/cnl: Simplify dco_fraction calculation.
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Git-commit: 8a00678a096445716861d2c0bd2a7007ad373f4d
Patch-mainline: v4.16-rc1
References: FATE#322643 bsc#1055900
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 Syrj채l채 <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 Syrj채l채 <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171115184257.8633-1-rodrigo.vivi@intel.com
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/gpu/drm/i915/intel_dpll_mgr.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
--- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
@@ -2153,6 +2153,8 @@ static void cnl_wrpll_params_populate(st
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(st
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