netdev - Re: Atheros 8035 PHY only works when at803x_config

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Message-ID: <55259FB5.50109@free.fr>
Date:	Wed, 08 Apr 2015 23:37:57 +0200
From:	Mason <slash.tmp@...e.fr>
To:	Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
CC:	Mugunthan <mugunthanvnm@...com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: Atheros 8035 PHY only works when at803x_config_init() is
 commented out

On 08/04/2015 19:29, Florian Fainelli wrote:
> On 08/04/15 09:28, Mason wrote:
>> Hello everyone,
>>
>> I have a weird problem, that I've only started investigating, and I'd be
>> grateful if anyone can help me along.
>>
>> I have an ARM-based SoC that provides (AFAIU) an Atheros 8035 PHY.
>>
>> If I enable the driver in my kernel (CONFIG_AT803X_PHY) then something
>> goes wrong, and the system cannot load the nfsroot. Bizarrely, DHCP
>> seems to work (so there is limited connectivity) but then the NFS
>> server just times out.
>>
>> However, if I just comment this line:
>>     //.config_init = at803x_config_init,
>> in at803x_driver[0]
>> then everything seems to work. (At least, the system sets the PHY
>> to Gbit, and manages to download the nfsroot.)
>>
>> If I'm reading the code right (big "if"), when config_init is NULL,
>> then phy_init_hw() turns into a NOP?
>>
>> So either at803x_config_init() or something called from phy_init_hw()
>> seems to be hosing this system's networking?
>>
>> Sprinkling printk over phy_init_hw shows no errors (no premature exit)
>> and phydev->drv->config_init(phydev) returns 0.
>>
>> Maybe I didn't set something up correctly, and phy_write() is scribbling
>> over the wrong register?
>>
>> Does anyone see something I missed?
> 
> So one possibility could be that the bootloader initializes the PHY in a
> certain way, typically by applying workarounds, and your config_init()
> callback is not restoring any of theses, which is why, after
> phy_init_hw(), which does a software reset of the PHY, all of these
> workarounds are wiped out, and your PHY behaves funky.
> 
> The reason why config_init() needs to put the PHY back into a fully
> functional state is because the PHY library should be able to software
> reset the PHY when it needs to, but also be able to deal with deep sleep
> modes etc.. where the PHY could loose its settings, yet the kernel
> should be able to bring you back in a good state.
> 
> An easy way to bypass that is to provide a soft_reset calback which does
> nothing, and see if calling either at803x_config_init(), or
> genphy_config_init() is sufficient to preserve the PHY settings.
> Although the real solution is to look at what the bootloader does on
> that front and replicate it in the config_init() callback.
> 
> Hope this helps.

Thanks for the insight. I hadn't considered the bootloader's role.

One thing I forgot to mention is that I'm using an old kernel 3.14
and it doesn't seem to have the soft_reset function pointer.

http://lxr.free-electrons.com/source/drivers/net/phy/phy_device.c?v=3.14#L535

phy_init_hw() just calls phy_write(phydev, MII_BMCR, BMCR_RESET)
and then phy_poll_reset(phydev) -- the equivalent of today's
genphy_soft_reset().

Anyway, I will look more closely at the points you mentioned.

Thanks again.

Regards.

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