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From:   Claudiu <claudiu.beznea@tuxon.dev>
To:     geert+renesas@glider.be, mturquette@baylibre.com, sboyd@kernel.org,
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Subject: [PATCH v2 05/28] clk: renesas: rzg2l: fix computation formula
Date:   Fri, 29 Sep 2023 08:38:52 +0300
Message-Id: <20230929053915.1530607-6-claudiu.beznea@bp.renesas.com>
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From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>

According to hardware manual of RZ/G2L (r01uh0914ej0130-rzg2l-rzg2lc.pdf)
the computation formula for PLL rate is as follows:

Fout = ((m + k/65536) * Fin) / (p * 2^s)

and k has values in range [-32768, 32767]. Dividing k by 65536 with
integer variables leads all the time to zero. Thus we may have slight
differences b/w what has been set vs. what is displayed. Thus,
get rid of this and decompose the formula before dividing k by 65536.

Fixes: ef3c613ccd68a ("clk: renesas: Add CPG core wrapper for RZ/G2L SoC")
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
---

Changes in v2:
- used mul_u64_u32_shr()

 drivers/clk/renesas/rzg2l-cpg.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/clk/renesas/rzg2l-cpg.c b/drivers/clk/renesas/rzg2l-cpg.c
index 6f50f0329ecf..f411e428196c 100644
--- a/drivers/clk/renesas/rzg2l-cpg.c
+++ b/drivers/clk/renesas/rzg2l-cpg.c
@@ -695,18 +695,18 @@ static unsigned long rzg2l_cpg_pll_clk_recalc_rate(struct clk_hw *hw,
 	struct pll_clk *pll_clk = to_pll(hw);
 	struct rzg2l_cpg_priv *priv = pll_clk->priv;
 	unsigned int val1, val2;
-	unsigned int mult = 1;
-	unsigned int div = 1;
+	u64 rate;
 
 	if (pll_clk->type != CLK_TYPE_SAM_PLL)
 		return parent_rate;
 
 	val1 = readl(priv->base + GET_REG_SAMPLL_CLK1(pll_clk->conf));
 	val2 = readl(priv->base + GET_REG_SAMPLL_CLK2(pll_clk->conf));
-	mult = MDIV(val1) + KDIV(val1) / 65536;
-	div = PDIV(val1) << SDIV(val2);
 
-	return DIV_ROUND_CLOSEST_ULL((u64)parent_rate * mult, div);
+	rate = mul_u64_u32_shr(parent_rate, (MDIV(val1) << 16) + (s16)KDIV(val1),
+			       16 + SDIV(val2));
+
+	return DIV_ROUND_CLOSEST_ULL(rate, PDIV(val1));
 }
 
 static const struct clk_ops rzg2l_cpg_pll_ops = {
-- 
2.39.2