2023-05-29 14:06:03

by Frank Oltmanns

Subject: [PATCH] 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(-)

diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
index 479297763e70..7da21cd2bdb1 100644
--- a/drivers/clk/clk-fractional-divider.c
+++ b/drivers/clk/clk-fractional-divider.c
@@ -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--;
--
2.40.1

2023-06-12 21:54:08

by Stephen Boyd

Subject: Re: [PATCH] clk: fractional-divider: Improve approximation when zero based

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

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?

2023-06-13 09:07:00

by Frank Oltmanns

Subject: Re: [PATCH] clk: fractional-divider: Improve approximation when zero based

Hi Stephen,

On 2023-06-12 at 14:39:00 -0700, Stephen Boyd <[email protected]> wrote:
> Quoting Frank Oltmanns (2023-05-29 06:34:33)
>> 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,
>
> 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