netdev - RE: [PATCH V1 net-next 0/3] net: stmmac: implement clocks

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Date:   Thu, 25 Feb 2021 01:42:59 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
CC:     "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "alexandre.torgue@...com" <alexandre.torgue@...com>,
        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH V1 net-next 0/3] net: stmmac: implement clocks


> -----Original Message-----
> From: Florian Fainelli <f.fainelli@...il.com>
> Sent: 2021年2月24日 11:54
> To: Joakim Zhang <qiangqing.zhang@....com>; Jakub Kicinski
> <kuba@...nel.org>
> Cc: peppe.cavallaro@...com; alexandre.torgue@...com;
> joabreu@...opsys.com; davem@...emloft.net; netdev@...r.kernel.org;
> dl-linux-imx <linux-imx@....com>
> Subject: Re: [PATCH V1 net-next 0/3] net: stmmac: implement clocks
> 
> 
> 
> On 2/23/2021 6:47 PM, Joakim Zhang wrote:
> >
> >> -----Original Message-----
> >> From: Jakub Kicinski <kuba@...nel.org>
> >> Sent: 2021年2月24日 10:35
> >> To: Joakim Zhang <qiangqing.zhang@....com>
> >> Cc: peppe.cavallaro@...com; alexandre.torgue@...com;
> >> joabreu@...opsys.com; davem@...emloft.net; netdev@...r.kernel.org;
> >> dl-linux-imx <linux-imx@....com>
> >> Subject: Re: [PATCH V1 net-next 0/3] net: stmmac: implement clocks
> >>
> >> On Wed, 24 Feb 2021 02:13:05 +0000 Joakim Zhang wrote:
> >>>>> The aim is to enable clocks when it needs, others keep clocks disabled.
> >>>>
> >>>> Understood. Please double check ethtool callbacks work fine. People
> >>>> often forget about those when disabling clocks in .close.
> >>>
> >>> Hi Jakub,
> >>>
> >>> If NIC is open then clocks are always enabled, so all ethtool
> >>> callbacks should be okay.
> >>>
> >>> Could you point me which ethtool callbacks could be invoked when NIC
> >>> is closed? I'm not very familiar with ethtool use case. Thanks.
> >>
> >> Well, all of them - ethtool does not check if the device is open.
> >> User can access and configure the device when it's closed.
> >> Often the callbacks access only driver data, but it's implementation
> >> specific so you'll need to validate the callbacks stmmac implements.
> >
> > Thanks Jakub, I will check these callbacks.
> 
> You can implement ethtool_ops::begin and ethtool_ops::complete where you
> would enable the clock, and respectively disable it just for the time of the
> operation. The ethtool framework guarantees that begin is called at the
> beginning and complete at the end. You can also make sure that if the interface
> is disabled you only return a cached copy of the settings/MIB counters (they
> are not updating since the HW is disabled) and conversely only store
> parameters in a cached structure and apply those when the network device
> gets opened again. Either way would work.

Hi Florian,

Thanks for you hint. Yes, I noticed stmmac driver has implemented ethtool_ops::begin, which let ethtool only can be used when interface is enabled. Thanks a lot.

Best Regards,
Joakim Zhang
> --
> Florian