linux-kernel - Re: [PATCH v2 1/3] net: mana: Add speed support in mana_get_link

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Message-ID: <20250421181412.GA5652@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Mon, 21 Apr 2025 11:14:12 -0700
From: Erni Sri Satya Vennela <ernis@...ux.microsoft.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com, andrew+netdev@...n.ch, davem@...emloft.net,
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	schakrabarti@...ux.microsoft.com, shradhagupta@...ux.microsoft.com,
	ssengar@...ux.microsoft.com, leon@...nel.org, rosenp@...il.com,
	paulros@...rosoft.com, linux-hyperv@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-rdma@...r.kernel.org
Subject: Re: [PATCH v2 1/3] net: mana: Add speed support in
 mana_get_link_ksettings

On Mon, Apr 21, 2025 at 02:36:43PM +0200, Andrew Lunn wrote:
> On Sun, Apr 20, 2025 at 11:33:38PM -0700, Erni Sri Satya Vennela wrote:
> > Add support for speed in mana ethtool get_link_ksettings
> > operation. This feature is not supported by all hardware.
> 
> This needs a lot more justification. tc(1) will show you the current
> HTB Qdisc setting. No other MAC driver i know of will show you Qdisc
> info in ksettings. So why is mana special?
> 
> Something your said in an earlier thread might be relevant here. There
> are two shaper settings involved. The Hypervisor can configure a
> limit, which the VM has no control over. And then you have this second
> limit the VM can set, which only has any effect if it is lower than
> the hypervisor limit.
> 
> The hypervisor limit is much more like the value ksettings represents,
> the media speed, which is impossible to go above, and the machine has
> no control over. Reporting that limit in ksettings would seem
> reasonable. But it does not appear your firmware offers that?
> 
>     Andrew
> 
Yes, that is correct. I will keep the ethtool mana_get_link_ksettings
unchanged, since the link speed can be reported using tc too. I will
make this change in the next version of the patch.
Thankyou for the pointer, Andrew.
> ---
> pw-bot: cr