Subject: Re: [PATCH net] net: dsa: microchip: fix initial port flush problem

From: Simon Horman <[email-masked]>
Date: Fri, 31 May 2024 20:02:34 +0100

On Tue, May 28, 2024 at 02:35:45PM -0700, [email-masked] wrote:
> From: Tristram Ha <[email-masked]>
> 
> The very first flush in any port will flush all learned addresses in all
> ports.  This can be observed by unplugging a cable from one port while
> additional ports are connected and dumping the fdb entries.
> 
> This problem is caused by the initially wrong value programmed to the
> register.  After the first flush the value is reset back to the normal so
> the next port flush will not cause such problem again.

Hi Tristram,

I think it would be worth spelling out why it is correct to:
1. Not set SW_FLUSH_STP_TABLE or SW_FLUSH_MSTP_TABLE; and
2. Preserve the value of the other bits of REG_SW_LUE_CTRL_1

> 
> Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
> Signed-off-by: Tristram Ha <[email-masked]>
> ---
>  drivers/net/dsa/microchip/ksz9477.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
> index f8ad7833f5d9..7cc92b90ffea 100644
> --- a/drivers/net/dsa/microchip/ksz9477.c
> +++ b/drivers/net/dsa/microchip/ksz9477.c
> @@ -356,8 +356,7 @@ int ksz9477_reset_switch(struct ksz_device *dev)
>  
>  	/* default configuration */
>  	ksz_read8(dev, REG_SW_LUE_CTRL_1, &data8);
> -	data8 = SW_AGING_ENABLE | SW_LINK_AUTO_AGING |
> -	      SW_SRC_ADDR_FILTER | SW_FLUSH_STP_TABLE | SW_FLUSH_MSTP_TABLE;
> +	data8 |= SW_AGING_ENABLE | SW_LINK_AUTO_AGING | SW_SRC_ADDR_FILTER;
>  	ksz_write8(dev, REG_SW_LUE_CTRL_1, data8);
>  
>  	/* disable interrupts */
> -- 
> 2.34.1
> 
>