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

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

[Florian Fainelli]

Implement the suspend/resume procedure for the Broadcom AC131 and BCM5241 type
of PHYs (10/100 only) by entering the standard power down followed by the
proprietary standby mode in the auxiliary mode 4 shadow register. On resume,
the PHY software reset is enough to make it come out of standby mode so we can
utilize brcm_fet_config_init() as the resume hook.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 drivers/net/phy/broadcom.c | 48 ++++++++++++++++++++++++++++++++++++++
 include/linux/brcmphy.h    |  1 +
 2 files changed, 49 insertions(+)

diff --git a/drivers/net/phy/broadcom.c b/drivers/net/phy/broadcom.c
index 31fbcdddc9ad..739348b3f135 100644
--- a/drivers/net/phy/broadcom.c
+++ b/drivers/net/phy/broadcom.c
@@ -766,6 +766,50 @@ static irqreturn_t brcm_fet_handle_interrupt(struct phy_device *phydev)
 	return IRQ_HANDLED;
 }
 
+static int brcm_fet_suspend(struct phy_device *phydev)
+{
+	int reg, err, err2, brcmtest;
+
+	/* We cannot use a read/modify/write here otherwise the PHY continues
+	 * to drive LEDs which defeats the purpose of low power mode.
+	 */
+	err = phy_write(phydev, MII_BMCR, BMCR_PDOWN);
+	if (err < 0)
+		return err;
+
+	/* Enable shadow register access */
+	brcmtest = phy_read(phydev, MII_BRCM_FET_BRCMTEST);
+	if (brcmtest < 0)
+		return brcmtest;
+
+	reg = brcmtest | MII_BRCM_FET_BT_SRE;
+
+	err = phy_write(phydev, MII_BRCM_FET_BRCMTEST, reg);
+	if (err < 0)
+		return err;
+
+	/* 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);
+	if (err < 0)
+		goto done;
+
+done:
+	/* Disable shadow register access */
+	err2 = phy_write(phydev, MII_BRCM_FET_BRCMTEST, brcmtest);
+	if (!err)
+		err = err2;
+
+	return err;
+}
+
 static int bcm54xx_phy_probe(struct phy_device *phydev)
 {
 	struct bcm54xx_phy_priv *priv;
@@ -1033,6 +1077,8 @@ static struct phy_driver broadcom_drivers[] = {
 	.config_init	= brcm_fet_config_init,
 	.config_intr	= brcm_fet_config_intr,
 	.handle_interrupt = brcm_fet_handle_interrupt,
+	.suspend	= brcm_fet_suspend,
+	.resume		= brcm_fet_config_init,
 }, {
 	.phy_id		= PHY_ID_BCM5241,
 	.phy_id_mask	= 0xfffffff0,
@@ -1041,6 +1087,8 @@ static struct phy_driver broadcom_drivers[] = {
 	.config_init	= brcm_fet_config_init,
 	.config_intr	= brcm_fet_config_intr,
 	.handle_interrupt = brcm_fet_handle_interrupt,
+	.suspend	= brcm_fet_suspend,
+	.resume		= brcm_fet_config_init,
 }, {
 	.phy_id		= PHY_ID_BCM5395,
 	.phy_id_mask	= 0xfffffff0,
diff --git a/include/linux/brcmphy.h b/include/linux/brcmphy.h
index 6ff567ece34a..9e77165f3ef6 100644
--- a/include/linux/brcmphy.h
+++ b/include/linux/brcmphy.h
@@ -293,6 +293,7 @@
 #define MII_BRCM_FET_SHDW_MC_FAME	0x4000	/* Force Auto MDIX enable */
 
 #define MII_BRCM_FET_SHDW_AUXMODE4	0x1a	/* Auxiliary mode 4 */
+#define MII_BRCM_FET_SHDW_AM4_STANDBY	0x0008	/* Standby enable */
 #define MII_BRCM_FET_SHDW_AM4_LED_MASK	0x0003
 #define MII_BRCM_FET_SHDW_AM4_LED_MODE1 0x0001
 
-- 
2.25.1

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

[Russell King (Oracle)]

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.

If it's sensitive to the timing of the read and the write, it suggests
the above code is fragile - maybe there needs to be a minimum delay
inserted between the read and the write?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

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

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

[Florian Fainelli]

On 8/15/22 11:09, Florian Fainelli wrote:
> 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?

Sorry, hit send too quickly, I see what problem you are referring to. v2 
coming up shortly utilizing phy_modify() and simplifying the return path 
(no need for done label, etc.)

Thanks
-- 
Florian