diff options
| author | Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> | 2023-05-24 11:28:01 +0300 |
|---|---|---|
| committer | Francesco Dolcini <francesco.dolcini@toradex.com> | 2023-06-19 15:54:19 +0200 |
| commit | cf089ee81460d586813143d0539955b3bf04caa3 (patch) | |
| tree | 26953485343c3e804335ef3a7b7f326f41b318ff | |
| parent | 6c81e4c96cfb50a47d62f45eccb68a2b160b1e87 (diff) | |
drm/bridge: tc358768: Cleanup PLL calculations
As is quite common, some of TC358768's PLL register fields are to be
programmed with (value - 1). Specifically, the FBD and PRD, multiplier
and divider, are such fields.
However, what the driver currently does is that it considers that the
formula used for PLL rate calculation is:
RefClk * [(FBD + 1)/ (PRD + 1)] * [1 / (2^FRS)]
where FBD and PRD are values directly from the registers, while a more
sensible way to look at it is:
RefClk * FBD / PRD * (1 / (2^FRS))
and when the FBD and PRD values are written to the registers, they will
be subtracted by one.
Change the driver accordingly, as it simplifies the PLL code.
Upstream-Status: Pending
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
| -rw-r--r-- | drivers/gpu/drm/bridge/tc358768.c | 14 |
1 files changed, 7 insertions, 7 deletions
diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c index 617c55fe3b27..9a418ea0d89b 100644 --- a/drivers/gpu/drm/bridge/tc358768.c +++ b/drivers/gpu/drm/bridge/tc358768.c @@ -313,7 +313,7 @@ static int tc358768_calc_pll(struct tc358768_priv *priv, target_pll = tc358768_pclk_to_pll(priv, mode->clock * 1000); - /* pll_clk = RefClk * [(FBD + 1)/ (PRD + 1)] * [1 / (2^FRS)] */ + /* pll_clk = RefClk * FBD / PRD * (1 / (2^FRS)) */ for (i = 0; i < ARRAY_SIZE(frs_limits); i++) if (target_pll >= frs_limits[i]) @@ -333,19 +333,19 @@ static int tc358768_calc_pll(struct tc358768_priv *priv, best_prd = 0; best_fbd = 0; - for (prd = 0; prd < 16; ++prd) { - u32 divisor = (prd + 1) * (1 << frs); + for (prd = 1; prd <= 16; ++prd) { + u32 divisor = prd * (1 << frs); u32 fbd; - for (fbd = 0; fbd < 512; ++fbd) { + for (fbd = 1; fbd <= 512; ++fbd) { u32 pll, diff, pll_in; - pll = (u32)div_u64((u64)refclk * (fbd + 1), divisor); + pll = (u32)div_u64((u64)refclk * fbd, divisor); if (pll >= max_pll || pll < min_pll) continue; - pll_in = (u32)div_u64((u64)refclk, prd + 1); + pll_in = (u32)div_u64((u64)refclk, prd); if (pll_in < 4000000) continue; @@ -608,7 +608,7 @@ static int tc358768_setup_pll(struct tc358768_priv *priv, mode->clock * 1000); /* PRD[15:12] FBD[8:0] */ - tc358768_write(priv, TC358768_PLLCTL0, (prd << 12) | fbd); + tc358768_write(priv, TC358768_PLLCTL0, ((prd - 1) << 12) | (fbd - 1)); /* FRS[11:10] LBWS[9:8] CKEN[4] RESETB[1] EN[0] */ tc358768_write(priv, TC358768_PLLCTL1, |