linux-kernel - Re: [PATCH RFT 0/8] Marvell PXA168 libphy handling and Berlin Ethernet

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Date:	Thu, 09 Oct 2014 09:57:35 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
CC:	devicetree@...r.kernel.org, Eric Miao <eric.y.miao@...il.com>,
	netdev@...r.kernel.org,
	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>, linux-kernel@...r.kernel.org,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFT 0/8] Marvell PXA168 libphy handling and Berlin Ethernet

On 10/09/2014 08:24 AM, Sebastian Hesselbarth wrote:
> On 10/09/2014 04:47 PM, Thomas Petazzoni wrote:
>> Well, I initially remember that the original driver coming from Marvell
>> was using the HW PHY stuff, and that I changed that because it would
>> not integrate well with the kernel libphy.
>>
>> A drawback of this is that because the hardware has built-in PHY
>> polling which triggers a MAC interrupt when the PHY status changes, they
>> typically don't wire up the PHY interrupt. Therefore, since we're not
>> able to use the MAC interrupt for PHY event notifications, we rely on
>> software PHY polling, which means that link up / link down events take
>> a few seconds to be noticed by the kernel. Unfortunately, I don't think
>> the hardware allows to use the hardware PHY polling to get link changes
>> interrupt, but not let the hardware configure the PHY itself.
> 
> Yeah, but that HW PHY stuff really only works properly with standard
> compliant PHYs. In particular, the integrated Marvell PHY in Marvell
> Berlin SoCs does not seem to reflect PHY status on BMCR properly /sigh/.
> Anyway, I think we can live with PHY polling.
> 
> BTW, one thing I noticed here is that libphy calls adjust_link
> over-and-over again although nothing has changed. I guess we can just
> add some before/after comparison in the libphy state machine and only
> call adjust_link when something has changed. I'll have to look closer
> at the state machine first and maybe Florian can comment on this,
> too.

There's basically nothing built in the generic libphy that would try to
limit the number of times the adjust_link() callback is invoked, some
changes went in the bcmgenet driver to avoid that, I have yet to see how
much of this logic is transferable to the libphy layer.
--
Florian
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