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

[Vladimir Oltean]

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.

> 
>  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.