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Message-ID: <4a467adcdb3ca8e272bd3ae1be54272610aabc9b.camel@redhat.com>
Date: Thu, 30 May 2024 11:13:00 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Tristram.Ha@...rochip.com, Arun Ramadoss <arun.ramadoss@...rochip.com>,
Woojung Huh <woojung.huh@...rochip.com>, Andrew Lunn <andrew@...n.ch>,
Vivien Didelot <vivien.didelot@...il.com>, Florian Fainelli
<f.fainelli@...il.com>, Vladimir Oltean <olteanv@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
UNGLinuxDriver@...rochip.com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: microchip: fix KSZ9477 set_ageing_time
function
On Tue, 2024-05-28 at 14:36 -0700, Tristram.Ha@...rochip.com wrote:
> From: Tristram Ha <tristram.ha@...rochip.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@...rochip.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
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