netdev - Re: [PATCH 2/2] net: qcom/emac: add software control for pause frame mode

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Message-ID: <9e7c0589-d163-a735-bb4c-87bc216164d2@codeaurora.org>
Date:   Tue, 1 Aug 2017 17:00:20 -0500
From:   Timur Tabi <timur@...eaurora.org>
To:     Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] net: qcom/emac: add software control for pause frame
 mode

On 08/01/2017 04:51 PM, Florian Fainelli wrote:

> A few adapters (bcmgenet, bcmsysport) support configuring the pause
> quanta so it would not be inconceivable to try to update
> ethtool_pauseparam to include additional fields such as:

Wouldn't this require a change to the user space tool?

> - number of pause frames to send where we define an arbitrary high
> default value (e.g: 0xffff), N < 0xffff is something drivers can test
> for whether they support it, and 0 is only valid if pause is already
> disabled
> 
> - pause quanta (16-bits)
> 
> Private flags are not usually that great and there could be more
> adapters capable of doing the same pause frame number configuration, but
> since there is no available knob it's hard to know.

Well, for the EMAC, the quanta in this case would be either 1 or 
infinite.  For other devices, it could be any combination of values.  In 
a future revision of the hardware, we might support a variable quanta. 
And I suspect that some devices measure the quanta in time, not count.

How would the user know what the acceptable values are?  If I set the 
quanta to 10 via user space, and my driver truncates that to 1, I don't 
think that would be acceptable.

-- 
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