netdev - Re: [RFC net-next 0/8] Introducing subdev bus and devlink extension

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Date:   Tue, 1 Jun 2021 14:34:51 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     moyufeng <moyufeng@...wei.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Parav Pandit <parav@...lanox.com>,
        Or Gerlitz <gerlitz.or@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "michal.lkml@...kovi.net" <michal.lkml@...kovi.net>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Jiri Pirko <jiri@...lanox.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        "lipeng (Y)" <lipeng321@...wei.com>,
        Guangbin Huang <huangguangbin2@...wei.com>,
        <shenjian15@...wei.com>, "chenhao (DY)" <chenhao288@...ilicon.com>,
        Jiaran Zhang <zhangjiaran@...wei.com>
Subject: Re: [RFC net-next 0/8] Introducing subdev bus and devlink extension

On Tue, 1 Jun 2021 15:33:09 +0800 Yunsheng Lin wrote:
> On 2021/6/1 13:37, Jakub Kicinski wrote:
> > On Mon, 31 May 2021 18:36:12 +0800 moyufeng wrote:  
> >> Hi, Jiri & Jakub
> >>
> >>     Generally, a devlink instance is created for each PF/VF. This
> >> facilitates the query and configuration of the settings of each
> >> function. But if some common objects, like the health status of
> >> the entire ASIC, the data read by those instances will be duplicate.
> >>
> >>     So I wonder do I just need to apply a public devlink instance for the
> >> entire ASIC to avoid reading the same data? If so, then I can't set
> >> parameters for each function individually. Or is there a better suggestion
> >> to implement it?  
> > 
> > I don't think there is a great way to solve this today. In my mind
> > devlink instances should be per ASIC, but I never had to solve this
> > problem for a multi-function ASIC.   
> 
> Is there a reason why it didn't have to be solved yet?
> Is it because the devices currently supporting devlink do not have
> this kind of problem, like single-function ASIC or multi-function
> ASIC without sharing common resource?

I'm not 100% sure, my guess is multi-function devices supporting
devlink are simple enough for the problem not to matter all that much.

> Was there a discussion how to solved it in the past?

Not really, we floated an idea of creating aliases for devlink
instances so a single devlink instance could answer to multiple 
bus identifiers. But nothing concrete.

> > Can you assume all functions are in the same control domain? Can they
> > trust each other?  
> 
> "same control domain" means if it is controlled by a single host, not
> by multi hosts, right?
> 
> If the PF is not passed through to a vm using VFIO and other PF is still
> in the host, then I think we can say it is controlled by a single host.
> 
> And each PF is trusted with each other right now, at least at the driver
> level, but not between VF.

Right, the challenge AFAIU is how to match up multiple functions into 
a single devlink instance, when driver has to probe them one by one.
If there is no requirement that different functions are securely
isolated it becomes a lot simpler (e.g. just compare device serial
numbers).