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SubjectRe: [PATCH NET v3 1/2] net: phy: Add phy loopback support in net phy framework
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On 2017/6/24 11:40, Yunsheng Lin wrote:
> Hi, Andrew
>
> On 2017/6/24 11:12, Andrew Lunn wrote:
>>> +int phy_loopback(struct phy_device *phydev, bool enable)
>>> +{
>>> + struct phy_driver *phydrv = to_phy_driver(phydev->mdio.dev.driver);
>>> + int ret = 0;
>>> +
>>> + if (enable && phydev->loopback_enabled)
>>> + return -EBUSY;
>>> +
>>> + if (!enable && !phydev->loopback_enabled)
>>> + return -EINVAL;
>>> +
>>> + if (phydev->drv && phydrv->set_loopback)
>>> + ret = phydrv->set_loopback(phydev, enable);
>>
>> else
>> ret = -EOPNOTSUPP;
>>
>>> +
>>> + if (ret)
>>> + return ret;
>>> +
>>> + phydev->loopback_enabled = enable;
>>> +
>>> + return 0;
>>> +}
>>> +EXPORT_SYMBOL(phy_loopback);
>>
>> One of the comments we made of the PHY code in the hns driver is that
>> its locking is completely broken. You have made the same error
>> here. The core needs to hold the mutex while calling into the PHY
>> driver.
> Do you mean hns_nic_config_phy_loopback need to hold the mutex while
> calling phy_loopback? and other place that calling phy_* function?
I took some time looking into how to take mutex in phy core, here is what
I find:
phy_resume call phydrv->resume without take mutex.
if phy driver implement resume function, for example marvell_resume, then

static int marvell_resume(struct phy_device *phydev)
{
int err;

/* Resume the fiber mode first */
if (!(phydev->supported & SUPPORTED_FIBRE)) {
err = phy_write(phydev, MII_MARVELL_PHY_PAGE, MII_M1111_FIBER);
if (err < 0)
goto error;

/* With the page set, use the generic resume */
err = genphy_resume(phydev);
if (err < 0)
goto error;

/* Then, the copper link */
err = phy_write(phydev, MII_MARVELL_PHY_PAGE, MII_M1111_COPPER);
if (err < 0)
goto error;
}

the code above executes without holding a mutex expect genphy_resume

/* With the page set, use the generic resume */
return genphy_resume(phydev);

error:
phy_write(phydev, MII_MARVELL_PHY_PAGE, MII_M1111_COPPER);
return err;
}

So I think the correct way to hold a lock is in phy_* function, not in genphy_*,
and current genphy_resume and phy_resume is broken in this way.
Please let me know if I misunderstand the mutex taking in phy core.

Best Regards
Yunsheng Lin

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