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Date: Thu, 8 Feb 2024 22:35:35 +0100
From: Andi Shyti <andi.shyti@kernel.org>
To: Piyush Malgujar <pmalgujar@marvell.com>
Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org, 
	sgarapati@marvell.com, cchavva@marvell.com, jannadurai@marvell.com
Subject: Re: [PATCH v3 1/4] i2c: thunderx: Clock divisor logic changes
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References: <20240206114349.32197-1-pmalgujar@marvell.com>
 <20240206114349.32197-2-pmalgujar@marvell.com>
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In-Reply-To: <20240206114349.32197-2-pmalgujar@marvell.com>

Hi Suneel and Piyush,

..

>  void octeon_i2c_set_clock(struct octeon_i2c *i2c)
>  {
>  	int tclk, thp_base, inc, thp_idx, mdiv_idx, ndiv_idx, foscl, diff;
> -	int thp = 0x18, mdiv = 2, ndiv = 0, delta_hz = 1000000;
> +	int mdiv_min = 2;

why is this int while all the other variables moved to be
"unsigned int"?

> +	/* starting value on search for lowest diff */
> +	const int huge_delta = INITIAL_DELTA_HZ;

this is not needed.

> +	/*
> +	 * Find divisors to produce target frequency, start with large delta
> +	 * to cover wider range of divisors, note thp = TCLK half period.
> +	 */
> +	unsigned int thp = 0x18, mdiv = 2, ndiv = 0, delta_hz = huge_delta;
> +
> +	if (octeon_i2c_is_otx2(to_pci_dev(i2c->dev))) {

you could save this in a boolean at the beginning and keep using
it.

> +		thp = 0x3;

as you are here, can we give a meaningful define to 0x18 and 0x3?

> +		mdiv_min = 0;
> +	}
>  
>  	for (ndiv_idx = 0; ndiv_idx < 8 && delta_hz != 0; ndiv_idx++) {
>  		/*
>  		 * An mdiv value of less than 2 seems to not work well
>  		 * with ds1337 RTCs, so we constrain it to larger values.
>  		 */
> -		for (mdiv_idx = 15; mdiv_idx >= 2 && delta_hz != 0; mdiv_idx--) {
> +		for (mdiv_idx = 15; mdiv_idx >= mdiv_min && delta_hz != 0; mdiv_idx--) {
>  			/*
>  			 * For given ndiv and mdiv values check the
>  			 * two closest thp values.
>  			 */
>  			tclk = i2c->twsi_freq * (mdiv_idx + 1) * 10;
>  			tclk *= (1 << ndiv_idx);
> -			thp_base = (i2c->sys_freq / (tclk * 2)) - 1;
> +			if (octeon_i2c_is_otx2(to_pci_dev(i2c->dev)))
> +				thp_base = (i2c->sys_freq / tclk) - 2;
> +			else
> +				thp_base = (i2c->sys_freq / (tclk * 2)) - 1;
>  
>  			for (inc = 0; inc <= 1; inc++) {
>  				thp_idx = thp_base + inc;
>  				if (thp_idx < 5 || thp_idx > 0xff)
>  					continue;
>  
> -				foscl = i2c->sys_freq / (2 * (thp_idx + 1));
> +				if (octeon_i2c_is_otx2(to_pci_dev(i2c->dev)))
> +					foscl = i2c->sys_freq / (thp_idx + 2);
> +				else
> +					foscl = i2c->sys_freq /
> +						(2 * (thp_idx + 1));

I need to trust you on this.

>  				foscl = foscl / (1 << ndiv_idx);
>  				foscl = foscl / (mdiv_idx + 1) / 10;
>  				diff = abs(foscl - i2c->twsi_freq);
> +				/* Use it if smaller diff from target */

can you please expand?

>  				if (diff < delta_hz) {
>  					delta_hz = diff;
>  					thp = thp_idx;
> diff --git a/drivers/i2c/busses/i2c-octeon-core.h b/drivers/i2c/busses/i2c-octeon-core.h
> index 9bb9f64fdda0392364638ecbaafe3fab5612baf6..694c24cecb7b144c1021549d1661b040c21bb998 100644
> --- a/drivers/i2c/busses/i2c-octeon-core.h
> +++ b/drivers/i2c/busses/i2c-octeon-core.h
> @@ -7,6 +7,7 @@
>  #include <linux/i2c-smbus.h>
>  #include <linux/io.h>
>  #include <linux/kernel.h>
> +#include <linux/pci.h>
>  
>  /* Controller command patterns */
>  #define SW_TWSI_V		BIT_ULL(63)	/* Valid bit */
> @@ -98,6 +99,8 @@ struct octeon_i2c_reg_offset {
>  #define TWSI_INT(x)	(x->roff.twsi_int)
>  #define SW_TWSI_EXT(x)	(x->roff.sw_twsi_ext)
>  
> +#define INITIAL_DELTA_HZ	1000000

This define doesn't need to be in the header, right? Can we move
it in the c file?

Andi