linux-kernel - Re: [RFC net-next v3 00/10] net: bridge: mrp: Add support for Media Redundancy Protocol (MRP)

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Message-ID: <20200218085522.630e4778@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Tue, 18 Feb 2020 08:55:22 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Allan W. Nielsen" <allan.nielsen@...rochip.com>
Cc:     Horatiu Vultur <horatiu.vultur@...rochip.com>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <bridge@...ts.linux-foundation.org>, <jiri@...nulli.us>,
        <ivecera@...hat.com>, <davem@...emloft.net>,
        <roopa@...ulusnetworks.com>, <nikolay@...ulusnetworks.com>,
        <anirudh.venkataramanan@...el.com>, <olteanv@...il.com>,
        <andrew@...n.ch>, <jeffrey.t.kirsher@...el.com>,
        <UNGLinuxDriver@...rochip.com>
Subject: Re: [RFC net-next v3 00/10]  net: bridge: mrp: Add support for
 Media Redundancy Protocol (MRP)

On Tue, 18 Feb 2020 13:18:11 +0100 Allan W. Nielsen wrote:
> But we should try make sure this also works in a backwards compatible
> way with future MRP aware HW, and with existing (and future) SwitchDev
> offloaded HW. At the very least we want to make this run on Ocelot, HW
> offload the MRC role, but do the MRM in SW (as the HW is not capable of
> this).
> 
> If we use the kernel to abstract the MRP forwarding (not the entire
> protocol like we did in v1/v2, not just the HW like we did in v3) then
> we will have more flxibility to support other HW with a different set of
> offload facilities, we can most likely achieve better performance, and
> it would be a cleaner design.
> 
> This will mean, that if user-space ask for MRP frame to be generated,
> the kernel should make sure it will happen. The kernel can try to
> offload this via the switchdev API, or it can do it in kernel-space.
> 
> Again, it will mean putting back some code into kernel space, but I
> think it is worth it.

FWIW having the guarantee that the kernel can always perform requested
service/operation (either thru offload or in SW in kernel space) seems
appealing and in line what we've been doing for other offloads. 

IOW it'd be nice to have a kernel space software fallback for the
offloaded operations.