linux-kernel - [PATCH V7 4/5] phy: freescale: fsl-samsung-hdmi: Use closest divider

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Message-ID: <20240911012838.944630-5-aford173@gmail.com>
Date: Tue, 10 Sep 2024 20:28:10 -0500
From: Adam Ford <aford173@...il.com>
To: linux-phy@...ts.infradead.org
Cc: dominique.martinet@...ark-techno.com,
	linux-imx@....com,
	festevam@...il.com,
	frieder.schrempf@...tron.de,
	aford@...conembedded.com,
	Sandor.yu@....com,
	Adam Ford <aford173@...il.com>,
	Vinod Koul <vkoul@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Marco Felsch <m.felsch@...gutronix.de>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	Lucas Stach <l.stach@...gutronix.de>,
	linux-kernel@...r.kernel.org
Subject: [PATCH V7 4/5] phy: freescale: fsl-samsung-hdmi: Use closest divider

Currently, if the clock values cannot be set to the exact rate,
the round_rate and set_rate functions use the closest value found in
the look-up-table.  In preparation of removing values from the LUT
that can be calculated evenly with the integer calculator, it's
necessary to ensure to check both the look-up-table and the integer
divider clock values to get the closest values to the requested
value.  It does this by measuring the difference between the
requested clock value and the closest value in both integer divider
calucator and the fractional clock look-up-table.

Which ever has the smallest difference between them is returned as
the closest rate.

Signed-off-by: Adam Ford <aford173@...il.com>
---
V7:  Because of the previous patch refactoring, the flow of this patch
     changed quite a bit to use more help functions and goto statements
     to hopefully make the code flow better and improve comment
     readability.  Because of the change, I removed s-o-b and r-b,
     and t-b tags.

V6:  Simplify the calculation of the closest rate and fix
     a situation where the integer divider values may not be properly
     setup before they are used.
     Fixup some comments
V5:  No Change
V4:  New to series
---
 drivers/phy/freescale/phy-fsl-samsung-hdmi.c | 40 ++++++++++++++------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
index 49317a96f767..67a28aac9c45 100644
--- a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
+++ b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
@@ -577,6 +577,16 @@ static void fsl_samsung_hdmi_calculate_phy(struct phy_config *cal_phy, unsigned
 	/* pll_div_regs 3-6 are fixed and pre-defined already */
 }
 
+static u32 fsl_samsung_hdmi_phy_get_closest_rate(unsigned long rate,
+						 u32 int_div_clk, u32 frac_div_clk)
+{
+	/* The int_div_clk may be greater than rate, so cast it and use ABS */
+	if (abs((long)rate - (long)int_div_clk) < (rate - frac_div_clk))
+		return int_div_clk;
+
+	return frac_div_clk;
+}
+
 static long phy_clk_round_rate(struct clk_hw *hw,
 			       unsigned long rate, unsigned long *parent_rate)
 {
@@ -624,27 +634,33 @@ static int phy_clk_set_rate(struct clk_hw *hw,
 		goto use_fract_div;
 
 	/*
-	 * If the rate from the fractional divder is not exact, check the integer divider,
+	 * If the rate from the fractional divider is not exact, check the integer divider,
 	 * and use it if that value is an exact match.
 	 */
 	int_div_clk = fsl_samsung_hdmi_phy_find_pms(rate, &p, &m, &s);
+	fsl_samsung_hdmi_calculate_phy(&calculated_phy_pll_cfg, int_div_clk, p, m, s);
 	if (int_div_clk == rate) {
-		dev_dbg(phy->dev, "fsl_samsung_hdmi_phy: integer divider rate = %u\n",
-				   int_div_clk);
-
-		fsl_samsung_hdmi_calculate_phy(&calculated_phy_pll_cfg, int_div_clk, p, m, s);
-		phy->cur_cfg  = &calculated_phy_pll_cfg;
-		return fsl_samsung_hdmi_phy_configure(phy, phy->cur_cfg);
+		goto use_int_div;
 	}
 
 	/*
-	 * If neither the fractional divder nor the integer divder can find an exact value
-	 * fall back to using the fractional divider
+	 * Compare the difference between the integer clock and the fractional clock against
+	 * the desired clock and which whichever is closest,
 	 */
+	if (fsl_samsung_hdmi_phy_get_closest_rate(rate, int_div_clk,
+						  fract_div_phy->pixclk) == fract_div_phy->pixclk)
+		goto use_fract_div;
+
+use_int_div:
+	dev_dbg(phy->dev, "fsl_samsung_hdmi_phy: integer divider rate = %u\n", int_div_clk);
+	phy->cur_cfg  = &calculated_phy_pll_cfg;
+	goto end;
+
 use_fract_div:
-	phy->cur_cfg = fract_div_phy;
-	dev_dbg(phy->dev, "fsl_samsung_hdmi_phy: using fractional divider rate = %u\n",
-			   phy->cur_cfg->pixclk);
+	 phy->cur_cfg = fract_div_phy;
+	 dev_dbg(phy->dev, "fsl_samsung_hdmi_phy: using fractional divider rate = %u\n",
+		   phy->cur_cfg->pixclk);
+end:
 	return fsl_samsung_hdmi_phy_configure(phy, phy->cur_cfg);
 }
 
-- 
2.43.0