[PATCH] clk: imx: pll14xx: fix recalc_rate for negative kdiv

[PATCH] clk: imx: pll14xx: fix recalc_rate for negative kdiv

[Kevin Groeneveld]

kdiv is a signed 16 bit value in the DEV_CTL1 register. Commit
53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation") changed
the kdiv variable from a short int to just int. When the value read from
the DIV_CTL1 register is assigned directly to an int the sign of the value
is lost resulting in incorrect results when the value is negative. Adding
a s16 cast to the register value fixes the issue.

Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation")
Signed-off-by: Kevin Groeneveld <kgroeneveld@lenbrook.com>
---
 drivers/clk/imx/clk-pll14xx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clk/imx/clk-pll14xx.c b/drivers/clk/imx/clk-pll14xx.c
index 1d0f79e9c346..d12194d17b10 100644
--- a/drivers/clk/imx/clk-pll14xx.c
+++ b/drivers/clk/imx/clk-pll14xx.c
@@ -254,7 +254,7 @@ static unsigned long clk_pll14xx_recalc_rate(struct clk_hw *hw,
 
 	if (pll->type == PLL_1443X) {
 		pll_div_ctl1 = readl_relaxed(pll->base + DIV_CTL1);
-		kdiv = FIELD_GET(KDIV_MASK, pll_div_ctl1);
+		kdiv = (s16)FIELD_GET(KDIV_MASK, pll_div_ctl1);
 	} else {
 		kdiv = 0;
 	}
-- 
2.17.1

Re: [PATCH] clk: imx: pll14xx: fix recalc_rate for negative kdiv

[Stephen Boyd]

Quoting Kevin Groeneveld (2022-12-10 12:38:35)
> kdiv is a signed 16 bit value in the DEV_CTL1 register. Commit
> 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation") changed
> the kdiv variable from a short int to just int. When the value read from
> the DIV_CTL1 register is assigned directly to an int the sign of the value
> is lost resulting in incorrect results when the value is negative. Adding

Can the field be negative?

> a s16 cast to the register value fixes the issue.
> 
> Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation")
> Signed-off-by: Kevin Groeneveld <kgroeneveld@lenbrook.com>

Re: [PATCH] clk: imx: pll14xx: fix recalc_rate for negative kdiv

[Kevin Groeneveld]

On 2023-02-10 18:24, Stephen Boyd wrote:
> Quoting Kevin Groeneveld (2022-12-10 12:38:35)
>> kdiv is a signed 16 bit value in the DEV_CTL1 register. Commit
>> 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation") changed
>> the kdiv variable from a short int to just int. When the value read from
>> the DIV_CTL1 register is assigned directly to an int the sign of the value
>> is lost resulting in incorrect results when the value is negative. Adding
> 
> Can the field be negative?

Yes it can be. That is how I found the issue as I had a negative value 
in imx_pll14xx_rate_table which used to work but broke with the above 
mentioned commit.

The i.MX8MM reference manual states:
 >Formula for Fraction PLLOUT:
 >* FOUT=((m+k/65536) x FIN) /(p x 2s)
 >* Where, 1 ≤ p ≤ 63, 64 ≤ m ≤ 1023, 0 ≤ s ≤ 6, -32768 ≤ k ≤ 32767
 >* p, m, and s are unsigned integers. k is a two's complement integer.

The comments in the imx_pll14xx_calc_settings function also mention the 
same range for kdiv. And this function also uses negative values. For 
example:

 >/* Then see if we can get the desired rate by only adjusting kdiv 
(glitch free) */
 >rate_min = pll14xx_calc_rate(pll, mdiv, pdiv, sdiv, KDIV_MIN, prate);
 >rate_max = pll14xx_calc_rate(pll, mdiv, pdiv, sdiv, KDIV_MAX, prate);

Where KDIV_MIN is defined as SHRT_MIN which is negative.


Kevin

Re: [PATCH] clk: imx: pll14xx: fix recalc_rate for negative kdiv

[Abel Vesa]

On 22-12-10 15:38:35, Kevin Groeneveld wrote:
> kdiv is a signed 16 bit value in the DEV_CTL1 register. Commit
> 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation") changed
> the kdiv variable from a short int to just int. When the value read from
> the DIV_CTL1 register is assigned directly to an int the sign of the value
> is lost resulting in incorrect results when the value is negative. Adding
> a s16 cast to the register value fixes the issue.
> 
> Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation")
> Signed-off-by: Kevin Groeneveld <kgroeneveld@lenbrook.com>

Reviewed-by: Abel Vesa <abel.vesa@linaro.org>

Stephen, can you pick this up through fixes?
> ---
>  drivers/clk/imx/clk-pll14xx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/imx/clk-pll14xx.c b/drivers/clk/imx/clk-pll14xx.c
> index 1d0f79e9c346..d12194d17b10 100644
> --- a/drivers/clk/imx/clk-pll14xx.c
> +++ b/drivers/clk/imx/clk-pll14xx.c
> @@ -254,7 +254,7 @@ static unsigned long clk_pll14xx_recalc_rate(struct clk_hw *hw,
>  
>  	if (pll->type == PLL_1443X) {
>  		pll_div_ctl1 = readl_relaxed(pll->base + DIV_CTL1);
> -		kdiv = FIELD_GET(KDIV_MASK, pll_div_ctl1);
> +		kdiv = (s16)FIELD_GET(KDIV_MASK, pll_div_ctl1);
>  	} else {
>  		kdiv = 0;
>  	}
> -- 
> 2.17.1
> 

Re: [PATCH] clk: imx: pll14xx: fix recalc_rate for negative kdiv

[Stephen Boyd]

Quoting Kevin Groeneveld (2022-12-10 12:38:35)
> kdiv is a signed 16 bit value in the DEV_CTL1 register. Commit
> 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation") changed
> the kdiv variable from a short int to just int. When the value read from
> the DIV_CTL1 register is assigned directly to an int the sign of the value
> is lost resulting in incorrect results when the value is negative. Adding
> a s16 cast to the register value fixes the issue.
> 
> Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation")
> Signed-off-by: Kevin Groeneveld <kgroeneveld@lenbrook.com>
> ---

Applied to clk-fixes