Re: [PATCH net-next] net: phy: broadcom: Implement suspend/resume for AC131 and BCM5241

[Florian Fainelli]

On 8/15/22 11:00, Russell King (Oracle) wrote:
> On Mon, Aug 15, 2022 at 10:43:56AM -0700, Florian Fainelli wrote:
> > +	/* We cannot use a read/modify/write here otherwise the PHY continues
> > +	 * to drive LEDs which defeats the purpose of low power mode.
> > +	 */
> ...
> > +	/* Set standby mode */
> > +	reg = phy_read(phydev, MII_BRCM_FET_SHDW_AUXMODE4);
> > +	if (reg < 0) {
> > +		err = reg;
> > +		goto done;
> > +	}
> > +
> > +	reg |= MII_BRCM_FET_SHDW_AM4_STANDBY;
> > +
> > +	err = phy_write(phydev, MII_BRCM_FET_SHDW_AUXMODE4, reg);
>
> Does the read-modify-write problem extend to this register? Why would
> the PHY behave differently whether you used phy_modify() here or not?
> On the mdio bus, it should be exactly the same - the only difference
> is that we're guaranteed to hold the lock over the sequence whereas
> this drops and re-acquires the lock.

What read-modify-write problem are you referring to, that is, are you 
talking about my statement about setting BMCR.PDOWN only or something else?

I could use phy_modify(), sure.
--
Florian