netdev - Re: [PATCH net-next] net: phy: check return code when requesting PHY driver module

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Message-ID: <a47c5dce-5b9a-6a58-a184-c0a250071b93@gmail.com>
Date:   Tue, 15 Jan 2019 22:52:00 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: check return code when requesting PHY
 driver module

On 15.01.2019 22:43, Andrew Lunn wrote:
> On Tue, Jan 15, 2019 at 09:33:52PM +0100, Heiner Kallweit wrote:
>> When requesting the PHY driver module fails we'll bind the genphy
>> driver later. This isn't obvious to the user and may cause, depending
>> on the PHY, different types of issues. Therefore check the return code
>> of request_module() and inform the user in case of failure.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
>> ---
>>  drivers/net/phy/phy_device.c | 17 +++++++++++++----
>>  1 file changed, 13 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
>> index a2423cbb2..1527ed0f2 100644
>> --- a/drivers/net/phy/phy_device.c
>> +++ b/drivers/net/phy/phy_device.c
>> @@ -548,6 +548,17 @@ static const struct device_type mdio_bus_phy_type = {
>>  	.pm = MDIO_BUS_PHY_PM_OPS,
>>  };
>>  
>> +static void phy_request_driver_module(struct phy_device *dev, int phy_id)
>> +{
>> +	int ret;
>> +
>> +	ret = request_module(MDIO_MODULE_PREFIX MDIO_ID_FMT,
>> +			     MDIO_ID_ARGS(phy_id));
>> +	if (IS_ENABLED(CONFIG_MODULES) && ret < 0)
>> +		phydev_err(dev, "error %d loading PHY driver module for ID 0x%08x\n",
>> +			   ret, phy_id);
>> +}
>> +
>>  struct phy_device *phy_device_create(struct mii_bus *bus, int addr, int phy_id,
>>  				     bool is_c45,
>>  				     struct phy_c45_device_ids *c45_ids)
>> @@ -610,12 +621,10 @@ struct phy_device *phy_device_create(struct mii_bus *bus, int addr, int phy_id,
>>  			if (!(c45_ids->devices_in_package & (1 << i)))
>>  				continue;
>>  
>> -			request_module(MDIO_MODULE_PREFIX MDIO_ID_FMT,
>> -				       MDIO_ID_ARGS(c45_ids->device_ids[i]));
>> +			phy_request_driver_module(dev, c45_ids->device_ids[i]);
> 
> Hi Heiner
> 
> I'm not sure this is a good idea for a c45 device. It can have
> multiple devices ids. All we really need is that a driver is loaded
> for one of them. That driver should then be able to control all the
> devices in the package. So i would probably only warn when all
> request_module() calls of failed.
> 
I explicitly check for ret < 0. If there's no PHY driver module for
a specific PHY ID then the return code would be > 0.
My understanding of request_module() is that a return code < 0
is returned if something bad happens in modprobe() call as such.

> Maybe it is actually better to warning when we bind the generic phy
> driver to the PHY? That is the real problem we are trying to warn
> about.
> 
There are several PHY's which don't need a dedicated driver because
they work perfectly fine with the generic PHY driver. Therefore I
think it's hard to tell between regular genphy usage and error when
binding the genphy driver.

> I also think reporting this as an error is too strong. Some PHYs are
> happy with the generic PHY driver. So i think a warning is better than
> an error.
> 
As stated above, the error message isn't triggered if there's no
PHY driver module for a PHY ID.

>    Andrew
> 
Heiner