netdev - Re: [PATCHv2 1/5] sh_eth: add generic wake-on-lan support via magic packet

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Message-ID: <87e3f9e6-0f5a-986c-772d-006cb25b9fd9@cogentembedded.com>
Date:   Sun, 18 Dec 2016 23:26:11 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Simon Horman <horms+renesas@...ge.net.au>,
        netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCHv2 1/5] sh_eth: add generic wake-on-lan support via magic
 packet

Hello.

On 12/12/2016 07:09 PM, Niklas Söderlund wrote:

> Add generic functionality to support Wake-on-Lan using MagicPacket which
> are supported by at least a few versions of sh_eth. Only add
> functionality for WoL, no specific sh_eth version are marked to support

    Versions.

> WoL yet.
>
> WoL is enabled in the suspend callback by setting MagicPacket detection
> and disabling all interrupts expect MagicPacket. In the resume path the
> driver needs to reset the hardware to rearm the WoL logic, this prevents
> the driver from simply restoring the registers and to take advantage of
> that sh_eth was not suspended to reduce resume time. To reset the
> hardware the driver close and reopens the device just like it would do

    Closes.

> in a normal suspend/resume scenario without WoL enabled, but it both
> close and open the device in the resume callback since the device needs

    Closes and opens.

> to be open for WoL to work.

> One quirk needed for WoL is that the module clock needs to be prevented
> from being switched off by Runtime PM. To keep the clock alive the

    I tried to find the code in question and failed, getting muddled in the 
RPM maze. Could you point at this code for my education? :-)

> suspend callback need to call clk_enable() directly to increase the

    My main concern is why we need to manipulate the clock directly --
can't you call RPM to achieve the same effect?

> usage count of the clock. Then when Runtime PM decreases the clock usage
> count it won't reach 0 and be switched off.

    You mean it does this even though we don't call pr_runtime_put_sync()
as done in sh_eth_close()?

> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
[...]

MBR, Sergei