RE: [PATCH v1 net] net: dsa: microchip: fix wrong register write when masking interrupt

[Tristram.Ha]

> Subject: Re: [PATCH v1 net] net: dsa: microchip: fix wrong register write when
> masking interrupt
> 
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> On Thu, May 30, 2024 at 06:39:13PM -0700, Tristram.Ha@xxxxxxxxxxxxx wrote:
> > From: Tristram Ha <tristram.ha@xxxxxxxxxxxxx>
> >
> > Initially the macro REG_SW_PORT_INT_MASK__4 is defined as 0x001C in
> > ksz9477_reg.h and REG_PORT_INT_MASK is defined as 0x#01F.  Because the
> > global and port interrupt handling is about the same the new
> > REG_SW_PORT_INT_MASK__1 is defined as 0x1F in ksz_common.h.  This works
> > as only the least significant bits have effect.  As a result the 32-bit
> > write needs to be changed to 8-bit.
> >
> > Fixes: e1add7dd6183 ("net: dsa: microchip: use common irq routines for girq and
> pirq")
> > Signed-off-by: Tristram Ha <tristram.ha@xxxxxxxxxxxxx>
> > ---
> > v1
> >  - clarify the reason to change the code
> 
> After v1 comes v2.

I thought the initial version starts at index 0?

> >
> >  drivers/net/dsa/microchip/ksz_common.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/dsa/microchip/ksz_common.c
> b/drivers/net/dsa/microchip/ksz_common.c
> > index 1e0085cd9a9a..3ad0879b00cd 100644
> > --- a/drivers/net/dsa/microchip/ksz_common.c
> > +++ b/drivers/net/dsa/microchip/ksz_common.c
> > @@ -2185,7 +2185,7 @@ static void ksz_irq_bus_sync_unlock(struct irq_data *d)
> >       struct ksz_device *dev = kirq->dev;
> >       int ret;
> >
> > -     ret = ksz_write32(dev, kirq->reg_mask, kirq->masked);
> > +     ret = ksz_write8(dev, kirq->reg_mask, kirq->masked);
> >       if (ret)
> >               dev_err(dev->dev, "failed to change IRQ mask\n");
> >
> > --
> > 2.34.1
> >
> 
> What is the user-visible functional impact of the 32-bit access? Justify
> why this is a bug worth sending to stable kernels please.
> 
> FWIW, struct ksz_irq operates on 16-bit registers.

As explained before the initial code uses register 0x1C but now it is
changed to 0x1F.

See the real operating code if not modified:

ret = ksz_write32(dev, 0x1F, 0x0000007F);

The original code looks like this:

ret = ksz_write32(dev, 0x1C, 0x0000007F);

BTW, all other KSZ switches except KSZ9897/KSZ9893 and LAN937X families
use only 8-bit access.