Re: [PATCH net v2 3/3] net: bcmgenet: synchronize UMAC_CMD access

[Doug Berger]

On 4/26/2024 11:19 AM, Florian Fainelli wrote:
> On 4/25/24 15:27, Doug Berger wrote:
> > The UMAC_CMD register is written from different execution
> > contexts and has insufficient synchronization protections to
> > prevent possible corruption. Of particular concern are the
> > acceses from the phy_device delayed work context used by the
> > adjust_link call and the BH context that may be used by the
> > ndo_set_rx_mode call.
> >
> > A spinlock is added to the driver to protect contended register
> > accesses (i.e. reg_lock) and it is used to synchronize accesses
> > to UMAC_CMD.
> >
> > Fixes: 1c1008c793fa ("net: bcmgenet: add main driver file")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
>
> Acked-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
>
> As a bug fix this is totally fine. I believe there could be an 
> improvement made in 'net-next' whereby we introduce an 
> unimac_rmw_locked() or something that essentially does:
>
> void unimac_rmw_locked(struct bcmgenet_priv *priv, u32 offset, u32 
> mask_clear, u32 mask_set)
> {
>      u32 reg;
>      spin_lock_bh(&priv->reg_lock);
>      reg = bcmgenet_umac_readl(priv, offset);
>      reg &= ~mask_clear;
>      reg |= mask_set;
>      bcmgenet_umac_writel(priv, reg, offset);
>      spin_unlock_bh(&priv->reg_lock);
> }
>
> At least a couple of callers could benefit from it. Thanks!
The only issue I see is enforcing the 2us delay in reset_umac(). A 
scenario where a different context might attempt to modify UMAC_CMD 
during that window is admittedly contrived, but the approach of this 
commit provides better protection.

-Doug