linux-kernel - Re: [PATCH net-next 25/28] [RFC] net: dpaa: Convert to phylink

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Date:   Sat, 18 Jun 2022 11:58:41 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Madalin Bucur <madalin.bucur@....com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next 25/28] [RFC] net: dpaa: Convert to phylink

Hi Russell,

On 6/18/22 4:22 AM, Russell King (Oracle) wrote:
> On Fri, Jun 17, 2022 at 08:45:38PM -0400, Sean Anderson wrote:
>> Hi Russell,
>>
>> Thanks for the quick response.
>> ...
>> Yes, I've been using the debug prints in phylink extensively as part of
>> debugging :)
>>
>> In this case, I added a debug statement to phylink_resolve printing out
>> cur_link_state, link_state.link, and pl->phy_state.link. I could see that
>> the phy link state was up and the mac (pcs) state was down. By inspecting
>> the PCS's registers, I determined that this was because AN had not completed
>> (in particular, the link was up in BMSR). I believe that forcing in-band-status
>> (by setting ovr_an_inband) shouldn't be necessary, but I was unable to get a link
>> up on any interface without it. In particular, the pre-phylink implementation
>> disabled PCS AN only for fixed links (which you can see in patch 23).
> 
> I notice that prior to patch 23, the advertisment register was set to
> 0x4001, but in phylink_mii_c22_pcs_encode_advertisement() we set it to
> 0x0001 (bit 14 being the acknowledge bit from the PCS to the PHY, which
> is normally managed by hardware.
> 
> It may be worth testing whether setting bit 14 changes the behaviour.

Thanks for the tip. I'll try that out on Monday.

--Sean