[PATCH net] net: dsa: microchip: fix KSZ9477 set_ageing_time function

[PATCH net] net: dsa: microchip: fix KSZ9477 set_ageing_time function

[Tristram.Ha]

From: Tristram Ha <tristram.ha@microchip.com>

The aging count is not a simple 11-bit value but comprises a 3-bit
multiplier and an 8-bit second count.  The code tries to find a set of
values with result close to the specifying value.

Note LAN937X has similar operation but provides an option to use
millisecond instead of second so there will be a separate fix in the
future.

Fixes: 2c119d9982b1 ("net: dsa: microchip: add the support for set_ageing_time")
Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
---
 drivers/net/dsa/microchip/ksz9477.c     | 64 +++++++++++++++++++++----
 drivers/net/dsa/microchip/ksz9477_reg.h |  1 -
 2 files changed, 54 insertions(+), 11 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index f8ad7833f5d9..1af11aee3119 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -1099,26 +1099,70 @@ void ksz9477_get_caps(struct ksz_device *dev, int port,
 int ksz9477_set_ageing_time(struct ksz_device *dev, unsigned int msecs)
 {
 	u32 secs = msecs / 1000;
+	u8 first, last, mult, i;
+	int min, ret;
+	int diff[8];
 	u8 value;
 	u8 data;
-	int ret;
 
-	value = FIELD_GET(SW_AGE_PERIOD_7_0_M, secs);
+	/* The aging timer comprises a 3-bit multiplier and an 8-bit second
+	 * value.  Either of them cannot be zero.  The maximum timer is then
+	 * 7 * 255 = 1785.
+	 */
+	if (!secs)
+		secs = 1;
 
-	ret = ksz_write8(dev, REG_SW_LUE_CTRL_3, value);
+	ret = ksz_read8(dev, REG_SW_LUE_CTRL_0, &value);
 	if (ret < 0)
 		return ret;
 
-	data = FIELD_GET(SW_AGE_PERIOD_10_8_M, secs);
+	/* Check whether there is need to update the multiplier. */
+	mult = FIELD_GET(SW_AGE_CNT_M, value);
+	if (mult > 0) {
+		/* Try to use the same multiplier already in the register. */
+		min = secs / mult;
+		if (min <= 0xff && min * mult == secs)
+			return ksz_write8(dev, REG_SW_LUE_CTRL_3, min);
+	}
 
-	ret = ksz_read8(dev, REG_SW_LUE_CTRL_0, &value);
-	if (ret < 0)
-		return ret;
+	/* Return error if too large. */
+	if (secs > 7 * 0xff)
+		return -EINVAL;
+
+	/* Find out which combination of multiplier * value results in a timer
+	 * value close to the specified timer value.
+	 */
+	first = (secs + 0xfe) / 0xff;
+	for (i = first; i <= 7; i++) {
+		min = secs / i;
+		diff[i] = secs - i * min;
+		if (!diff[i]) {
+			i++;
+			break;
+		}
+	}
+
+	last = i;
+	min = 0xff;
+	for (i = last - 1; i >= first; i--) {
+		if (diff[i] < min) {
+			data = i;
+			min = diff[i];
+		}
+		if (!min)
+			break;
+	}
 
-	value &= ~SW_AGE_CNT_M;
-	value |= FIELD_PREP(SW_AGE_CNT_M, data);
+	if (mult != data) {
+		value &= ~SW_AGE_CNT_M;
+		value |= FIELD_PREP(SW_AGE_CNT_M, data);
+		ret = ksz_write8(dev, REG_SW_LUE_CTRL_0, value);
+		if (ret)
+			return ret;
+	}
 
-	return ksz_write8(dev, REG_SW_LUE_CTRL_0, value);
+	value = secs / data;
+	return ksz_write8(dev, REG_SW_LUE_CTRL_3, value);
 }
 
 void ksz9477_port_queue_split(struct ksz_device *dev, int port)
diff --git a/drivers/net/dsa/microchip/ksz9477_reg.h b/drivers/net/dsa/microchip/ksz9477_reg.h
index f3a205ee483f..0c55a540f20d 100644
--- a/drivers/net/dsa/microchip/ksz9477_reg.h
+++ b/drivers/net/dsa/microchip/ksz9477_reg.h
@@ -171,7 +171,6 @@
 #define SW_DROP_INVALID_VID		BIT(6)
 #define SW_AGE_CNT_M			GENMASK(5, 3)
 #define SW_AGE_CNT_S			3
-#define SW_AGE_PERIOD_10_8_M		GENMASK(10, 8)
 #define SW_RESV_MCAST_ENABLE		BIT(2)
 #define SW_HASH_OPTION_M		0x03
 #define SW_HASH_OPTION_CRC		1
-- 
2.34.1

Re: [PATCH net] net: dsa: microchip: fix KSZ9477 set_ageing_time function

[Paolo Abeni]

On Tue, 2024-05-28 at 14:36 -0700, Tristram.Ha@microchip.com wrote:
> From: Tristram Ha <tristram.ha@microchip.com>
> 
> The aging count is not a simple 11-bit value but comprises a 3-bit
> multiplier and an 8-bit second count.  The code tries to find a set of
> values with result close to the specifying value.
> 
> Note LAN937X has similar operation but provides an option to use
> millisecond instead of second so there will be a separate fix in the
> future.
> 
> Fixes: 2c119d9982b1 ("net: dsa: microchip: add the support for set_ageing_time")
> Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
> ---
>  drivers/net/dsa/microchip/ksz9477.c     | 64 +++++++++++++++++++++----
>  drivers/net/dsa/microchip/ksz9477_reg.h |  1 -
>  2 files changed, 54 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
> index f8ad7833f5d9..1af11aee3119 100644
> --- a/drivers/net/dsa/microchip/ksz9477.c
> +++ b/drivers/net/dsa/microchip/ksz9477.c
> @@ -1099,26 +1099,70 @@ void ksz9477_get_caps(struct ksz_device *dev, int port,
>  int ksz9477_set_ageing_time(struct ksz_device *dev, unsigned int msecs)
>  {
>  	u32 secs = msecs / 1000;
> +	u8 first, last, mult, i;
> +	int min, ret;
> +	int diff[8];
>  	u8 value;
>  	u8 data;
> -	int ret;
>  
> -	value = FIELD_GET(SW_AGE_PERIOD_7_0_M, secs);
> +	/* The aging timer comprises a 3-bit multiplier and an 8-bit second
> +	 * value.  Either of them cannot be zero.  The maximum timer is then
> +	 * 7 * 255 = 1785.
> +	 */
> +	if (!secs)
> +		secs = 1;
>  
> -	ret = ksz_write8(dev, REG_SW_LUE_CTRL_3, value);
> +	ret = ksz_read8(dev, REG_SW_LUE_CTRL_0, &value);
>  	if (ret < 0)
>  		return ret;
>  
> -	data = FIELD_GET(SW_AGE_PERIOD_10_8_M, secs);
> +	/* Check whether there is need to update the multiplier. */
> +	mult = FIELD_GET(SW_AGE_CNT_M, value);
> +	if (mult > 0) {
> +		/* Try to use the same multiplier already in the register. */
> +		min = secs / mult;
> +		if (min <= 0xff && min * mult == secs)
> +			return ksz_write8(dev, REG_SW_LUE_CTRL_3, min);
> +	}
>  
> -	ret = ksz_read8(dev, REG_SW_LUE_CTRL_0, &value);
> -	if (ret < 0)
> -		return ret;
> +	/* Return error if too large. */
> +	if (secs > 7 * 0xff)
> +		return -EINVAL;
> +
> +	/* Find out which combination of multiplier * value results in a timer
> +	 * value close to the specified timer value.
> +	 */
> +	first = (secs + 0xfe) / 0xff;
> +	for (i = first; i <= 7; i++) {
> +		min = secs / i;
> +		diff[i] = secs - i * min;
> +		if (!diff[i]) {
> +			i++;
> +			break;
> +		}
> +	}
> +
> +	last = i;
> +	min = 0xff;
> +	for (i = last - 1; i >= first; i--) {
> +		if (diff[i] < min) {
> +			data = i;
> +			min = diff[i];
> +		}
> +		if (!min)
> +			break;
> +	}

Is the additional accuracy worthy the added complexity WRT:

	mult = DIV_ROUND_UP(secs, 0xff);

?

Paolo

RE: [PATCH net] net: dsa: microchip: fix KSZ9477 set_ageing_time function

[Tristram.Ha]

> Subject: Re: [PATCH net] net: dsa: microchip: fix KSZ9477 set_ageing_time function
> 
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content
> is safe
> 
> On Tue, 2024-05-28 at 14:36 -0700, Tristram.Ha@microchip.com wrote:
> > From: Tristram Ha <tristram.ha@microchip.com>
> >
> > The aging count is not a simple 11-bit value but comprises a 3-bit
> > multiplier and an 8-bit second count.  The code tries to find a set of
> > values with result close to the specifying value.
> >
> > Note LAN937X has similar operation but provides an option to use
> > millisecond instead of second so there will be a separate fix in the
> > future.
> >
> > Fixes: 2c119d9982b1 ("net: dsa: microchip: add the support for set_ageing_time")
> > Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
> > ---
> >  drivers/net/dsa/microchip/ksz9477.c     | 64 +++++++++++++++++++++----
> >  drivers/net/dsa/microchip/ksz9477_reg.h |  1 -
> >  2 files changed, 54 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/net/dsa/microchip/ksz9477.c
> b/drivers/net/dsa/microchip/ksz9477.c
> > index f8ad7833f5d9..1af11aee3119 100644
> > --- a/drivers/net/dsa/microchip/ksz9477.c
> > +++ b/drivers/net/dsa/microchip/ksz9477.c
> > @@ -1099,26 +1099,70 @@ void ksz9477_get_caps(struct ksz_device *dev, int
> port,
> >  int ksz9477_set_ageing_time(struct ksz_device *dev, unsigned int msecs)
> >  {
> >       u32 secs = msecs / 1000;
> > +     u8 first, last, mult, i;
> > +     int min, ret;
> > +     int diff[8];
> >       u8 value;
> >       u8 data;
> > -     int ret;
> >
> > -     value = FIELD_GET(SW_AGE_PERIOD_7_0_M, secs);
> > +     /* The aging timer comprises a 3-bit multiplier and an 8-bit second
> > +      * value.  Either of them cannot be zero.  The maximum timer is then
> > +      * 7 * 255 = 1785.
> > +      */
> > +     if (!secs)
> > +             secs = 1;
> >
> > -     ret = ksz_write8(dev, REG_SW_LUE_CTRL_3, value);
> > +     ret = ksz_read8(dev, REG_SW_LUE_CTRL_0, &value);
> >       if (ret < 0)
> >               return ret;
> >
> > -     data = FIELD_GET(SW_AGE_PERIOD_10_8_M, secs);
> > +     /* Check whether there is need to update the multiplier. */
> > +     mult = FIELD_GET(SW_AGE_CNT_M, value);
> > +     if (mult > 0) {
> > +             /* Try to use the same multiplier already in the register. */
> > +             min = secs / mult;
> > +             if (min <= 0xff && min * mult == secs)
> > +                     return ksz_write8(dev, REG_SW_LUE_CTRL_3, min);
> > +     }
> >
> > -     ret = ksz_read8(dev, REG_SW_LUE_CTRL_0, &value);
> > -     if (ret < 0)
> > -             return ret;
> > +     /* Return error if too large. */
> > +     if (secs > 7 * 0xff)
> > +             return -EINVAL;
> > +
> > +     /* Find out which combination of multiplier * value results in a timer
> > +      * value close to the specified timer value.
> > +      */
> > +     first = (secs + 0xfe) / 0xff;
> > +     for (i = first; i <= 7; i++) {
> > +             min = secs / i;
> > +             diff[i] = secs - i * min;
> > +             if (!diff[i]) {
> > +                     i++;
> > +                     break;
> > +             }
> > +     }
> > +
> > +     last = i;
> > +     min = 0xff;
> > +     for (i = last - 1; i >= first; i--) {
> > +             if (diff[i] < min) {
> > +                     data = i;
> > +                     min = diff[i];
> > +             }
> > +             if (!min)
> > +                     break;
> > +     }
> 
> Is the additional accuracy worthy the added complexity WRT:
> 
>         mult = DIV_ROUND_UP(secs, 0xff);
> 
> ?

I do not know much accuracy is expected of this function.  I do not know
whether users can easily specify the amount, but the default is 3 seconds
which is the same as the hardware default where the multiplier is 4 and
the count is 75.  So most of the time the rest of the code will not be
executed.

Re: [PATCH net] net: dsa: microchip: fix KSZ9477 set_ageing_time function

[Andrew Lunn]

> > Is the additional accuracy worthy the added complexity WRT:
> > 
> >         mult = DIV_ROUND_UP(secs, 0xff);
> > 
> > ?
> 
> I do not know much accuracy is expected of this function.  I do not know
> whether users can easily specify the amount, but the default is 3 seconds
> which is the same as the hardware default where the multiplier is 4 and
> the count is 75.  So most of the time the rest of the code will not be
> executed.

Are you sure it is 3 seconds?

#define BR_DEFAULT_AGEING_TIME	(300 * HZ)

Fast ageing, after a topology change, is i think 15 seconds.

     Andrew