Unverified Commit 1e08e788 authored by Tomi Valkeinen's avatar Tomi Valkeinen Committed by Robert Foss
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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.

Reviewed-by: default avatarPeter Ujfalusi <peter.ujfalusi@gmail.com>
Tested-by: Maxim Schwalm <maxim.schwalm@gmail.com> # Asus TF700T
Tested-by: default avatarMarcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: default avatarTomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: default avatarRobert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230906-tc358768-v4-5-31725f008a50@ideasonboard.com
parent 66962d5c

drivers/gpu/drm/bridge/tc358768.c

+7 −7
Original line number Diff line number Diff line
@@ -316,7 +316,7 @@ 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])
@@ -336,19 +336,19 @@ 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;
@@ -611,7 +611,7 @@ 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,