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

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Message-ID: <5436C5C6.3020406@gmail.com>
Date:	Thu, 09 Oct 2014 19:28:38 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Florian Fainelli <f.fainelli@...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 06:57 PM, Florian Fainelli wrote:
> On 10/09/2014 08:24 AM, Sebastian Hesselbarth wrote:
>> 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.

Ok, thanks for the clarification. I guess for the final patch series,
I'll add a check for both registers modified in foo_adjust_link to bail
out if there is no change. That will save the two register writes per
second or so and also allow to phy_print_status() after the writels.

Sebastian
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