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

[<Tristram.Ha@microchip.com>]

> Subject: Re: [PATCH net] net: dsa: microchip: fix initial port flush problem
> 
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> On Tue, May 28, 2024 at 02:35:45PM -0700, Tristram.Ha@microchip.com wrote:
> > From: Tristram Ha <tristram.ha@microchip.com>
> >
> > 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

Setting SW_FLUSH_STP_TABLE and SW_FLUSH_MSTP_TABLE bits are wrong as they
are action bits.  The bit should be set only when doing an action like
flushing.

> >
> > Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
> > Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
> > ---
> >  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
> >
> >