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clk: fractional-divider: Improve approximation when zero based

PATCH Superseded Frank Oltmanns 2 participants 3 messages May 29, 2023 – Jun 13, 2023 Common clk

v1 of 5 Superseded Latest is v5 →

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Frank Oltmanns

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#0 lore raw

PATCH 1/1 clk: fractional-divider: Improve approximation when zero based

Consider the CLK_FRAC_DIVIDER_ZERO_BASED flag when finding the best approximation for m and n. By doing so, increase the range of valid values for the numerator and denominator by 1.

Cc A.s. Dong <[email protected]
Signed-off-by Frank Oltmanns <[email protected]>

---
I stumpled upon this, when familiarizing myself with clk drivers. Unfortunately, I have no boards to test this patch. It seems the only user of this flag in mainline is drivers/clk/imx/clk-composite-7ulp.c, therefore I'm cc-ing get_maintainers.pl --git-blame -f drivers/clk/imx/clk-composite-7ulp.c in the hopes of a wider audience.

Thank you for considering this contribution,
Frank

 drivers/clk/clk-fractional-divider.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)
drivers/clk/clk-fractional-divider.c +19 -7
index 479297763e70..7da21cd2bdb1 100644
@@ -123,6 +123,7 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw,
 						  unsigned long *m, unsigned long *n)
 {
 	struct clk_fractional_divider *fd = to_clk_fd(hw);
+	unsigned long max_m, max_n;
 
 	/*
 	 * Get rate closer to *parent_rate to guarantee there is no overflow

@@ -138,9 +139,15 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw,
 			rate <<= scale - fd->nwidth;
 	}
 
-	rational_best_approximation(rate, *parent_rate,
-			GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
-			m, n);
+	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
+		max_m = 1 << fd->mwidth;
+		max_n = 1 << fd->nwidth;
+	} else {
+		max_m = GENMASK(fd->mwidth - 1, 0);
+		max_n = GENMASK(fd->nwidth - 1, 0);
+	}
+
+	rational_best_approximation(rate, *parent_rate, max_m, max_n, m, n);
 }
 
 static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,

@@ -169,13 +176,18 @@ static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
 {
 	struct clk_fractional_divider *fd = to_clk_fd(hw);
 	unsigned long flags = 0;
-	unsigned long m, n;
+	unsigned long m, n, max_m, max_n;
 	u32 mmask, nmask;
 	u32 val;
 
-	rational_best_approximation(rate, parent_rate,
-			GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
-			&m, &n);
+	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
+		max_m = 1 << fd->mwidth;
+		max_n = 1 << fd->nwidth;
+	} else {
+		max_m = GENMASK(fd->mwidth - 1, 0);
+		max_n = GENMASK(fd->nwidth - 1, 0);
+	}
+	rational_best_approximation(rate, parent_rate, max_m, max_n, &m, &n);
 
 	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
 		m--;
Signature · 1 line
2.40.1
maintainer
#1 lore raw

Quoting Frank Oltmanns (2023-05-29 06:34:33)

Quoted 6 lines

Consider the CLK_FRAC_DIVIDER_ZERO_BASED flag when finding the best approximation for m and n. By doing so, increase the range of valid values for the numerator and denominator by 1.

Cc A.s. Dong <[email protected]
Signed-off-by Frank Oltmanns <[email protected]>
Quoted 8 lines

---
I stumpled upon this, when familiarizing myself with clk drivers. Unfortunately, I have no boards to test this patch. It seems the only user of this flag in mainline is drivers/clk/imx/clk-composite-7ulp.c, therefore I'm cc-ing get_maintainers.pl --git-blame -f drivers/clk/imx/clk-composite-7ulp.c in the hopes of a wider audience.

Thank you for considering this contribution,

Thanks for looking at this. Can you add a kunit test (or a suite of tests) to confirm that this doesn't break existing functionality and also improves a case that would have failed or been suboptimal before?

author
#2 lore raw

Hi Stephen,

Quoted 14 lines · Stephen Boyd

Quoting Frank Oltmanns (2023-05-29 06:34:33)

Quoted 13 lines

Consider the CLK_FRAC_DIVIDER_ZERO_BASED flag when finding the best approximation for m and n. By doing so, increase the range of valid values for the numerator and denominator by 1.

Cc A.s. Dong <[email protected]
Signed-off-by Frank Oltmanns <[email protected]>

---
I stumpled upon this, when familiarizing myself with clk drivers. Unfortunately, I have no boards to test this patch. It seems the only user of this flag in mainline is drivers/clk/imx/clk-composite-7ulp.c, therefore I'm cc-ing get_maintainers.pl --git-blame -f drivers/clk/imx/clk-composite-7ulp.c in the hopes of a wider audience.

Quoted 5 lines
Quoted 1 line

Thank you for considering this contribution,

Thanks for looking at this. Can you add a kunit test (or a suite of tests) to confirm that this doesn't break existing functionality and also improves a case that would have failed or been suboptimal before?

Thank you for your feedback, I've submitted a V2 that contains the tests:

https://lore.kernel.org/lkml/[email protected]/

Thanks,
Frank

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