Re: [PATCH v2 4/4] wifi: ath12k: fix dest ring-buffer corruption when ring is full

[Johan Hovold <johan@kernel.org>]

On Fri, Jun 06, 2025 at 03:27:04PM +0800, Miaoqing Pan wrote:
> On 6/4/2025 10:45 PM, Johan Hovold wrote:
> > Add the missing memory barriers to make sure that destination ring
> > descriptors are read before updating the tail pointer (and passing
> > ownership to the device) to avoid memory corruption on weakly ordered
> > architectures like aarch64 when the ring is full.

> > @@ -2184,6 +2187,10 @@ void ath12k_hal_srng_access_end(struct ath12k_base *ab, struct hal_srng *srng)
> >   					   srng->u.src_ring.hp);
> >   		} else {
> >   			srng->u.dst_ring.last_hp = *srng->u.dst_ring.hp_addr;
> > +			/* Make sure descriptor is read before updating the
> > +			 * tail pointer.
> > +			 */
> > +			mb();
> 
> Is rmb() sufficient, since MMIO write already includes wmb()?

No, rmb() only orders reads against later reads.

[ The wmb() itself orders reads against later writes on aarch64, but
that's not generally guaranteed and hence should not be relied on in
driver code. ]

> >   			ath12k_hif_write32(ab,
> >   					   (unsigned long)srng->u.dst_ring.tp_addr -
> >   					   (unsigned long)ab->mem,

Johan