netdev - Re: [PATCH] Revert "phy: add support for a reset-gpio specification"

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Date:	Thu, 19 May 2016 20:11:22 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Guenter Roeck <linux@...ck-us.net>,
	Fabio Estevam <fabio.estevam@....com>, davem@...emloft.net
Cc:	u.kleine-koenig@...gutronix.de, f.fainelli@...il.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] Revert "phy: add support for a reset-gpio specification"

Hello.

On 05/19/2016 04:29 PM, Guenter Roeck wrote:

>>> Commit da47b4572056 ("phy: add support for a reset-gpio specification")
>>> causes the following xtensa qemu crash according to Guenter Roeck:
>>>
>>> [    9.366256] libphy: ethoc-mdio: probed
>>> [    9.367389]  (null): could not attach to PHY
>>> [    9.368555]  (null): failed to probe MDIO bus
>>> [    9.371540] Unable to handle kernel paging request at virtual address
>>> 0000001c
>>> [    9.371540]  pc = d0320926, ra = 903209d1
>>> [    9.375358] Oops: sig: 11 [#1]
>>
>>     Of course, I'd like this patch to be reverted (as it was applied
>> erroneously instead of my patches)... but where's the backtrace? It's not
>> immediately clear how this code can cause kernel oops...
>>
> See http://www.spinics.net/lists/kernel/msg2258611.html.

    OK, I'll try to comment on your analysis posted there:

> GPIOLIB is not configured in my test case, meaning gpiod_get_optional()
> returns -ENOSYS, and phy_probe() thus returns an error. Question here is if
> it is really appropriate for the XXX_optional() gpiolib functions to return
> an error if GPIOLIB is not configured. Either case, result is that pretty
> much all phy registrations will now fail if GPIOLIB is not configured.

    Yes, that's the primary issue. That's what needs to be fixed...

> Also, I suspect that there may be a bug in the error handling path
> of ethoc_probe(). No idea what exactly is wrong, though. Other drivers
> use pretty much the same code sequence for mdio registration and associated
> error handling.

    I tried analyzing this code and it wasn't clear what's the issue...
    I must mention that this code actually looked strange -- other drivers 
call phy_connect_direct() etc. from their ndo_open() method, this driver does 
this from the probe. One problem I'm seing is that iff register_netdev() 
fails, it forgets to disconnect from the PHY.

> Last but not least, something seems to be wrong with the use of dev_err()
> with &netdev->dev if register_netdev() has not yet been called. Maybe someone
> has some insight ?

    Yes, this needs fixing as well.

> Guenter

MBR, Sergei