netdev - Re: [PATCH net-next 2/9] ice: devlink PF MSI-X max and min parameter

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Message-ID: <20250204184121.168eaba2@pumpkin>
Date: Tue, 4 Feb 2025 18:41:21 +0000
From: David Laight <david.laight.linux@...il.com>
To: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com,
 andrew+netdev@...n.ch, netdev@...r.kernel.org, sridhar.samudrala@...el.com,
 jacob.e.keller@...el.com, pio.raczynski@...il.com,
 konrad.knitter@...el.com, marcin.szycik@...el.com,
 nex.sw.ncis.nat.hpm.dev@...el.com, przemyslaw.kitszel@...el.com,
 jiri@...nulli.us, horms@...nel.org, David.Laight@...lab.com,
 pmenzel@...gen.mpg.de, mschmidt@...hat.com, tatyana.e.nikolova@...el.com,
 Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
 linux-rdma@...r.kernel.org, corbet@....net, linux-doc@...r.kernel.org
Subject: Re: [PATCH net-next 2/9] ice: devlink PF MSI-X max and min
 parameter

On Tue, 4 Feb 2025 07:06:00 +0100
Michal Swiatkowski <michal.swiatkowski@...ux.intel.com> wrote:

> On Mon, Feb 03, 2025 at 09:48:08PM +0000, David Laight wrote:
> > On Mon,  3 Feb 2025 13:09:31 -0800
> > Tony Nguyen <anthony.l.nguyen@...el.com> wrote:
> >   
> > > From: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
> > > 
> > > Use generic devlink PF MSI-X parameter to allow user to change MSI-X
> > > range.
> > > 
> > > Add notes about this parameters into ice devlink documentation.
....
> > Don't those checks make it difficult to set the min and max together?
> > I think you need to create the new min/max pair and check they are
> > valid together.
> > Which probably requires one parameter with two values.
> >   
> 
> I wanted to reuse exsisting parameter. The other user of it is bnxt
> driver. In it there is a separate check for min "max" and max "max".
> It is also problematic, because min can be set to value greater than
> max (here it can happen when setting together to specific values).
> I can do a follow up to this series and change this parameter as you
> suggested. What do you think?

Changing the way a parameter is used will break API compatibility.
Perhaps you can get the generic parameter validation function to
update a 'pending' copy, and then do the final min < max check after
all the parameters have been processed before actually updating
the live limits.

The other option is just not to check whether min < max and just
document which takes precedence (and not use clamp()).

It may even be worth saving the 'live limits' as 'hi << 16 | lo' so
that then can be accessed atomically (with READ/WRITE_ONCE) to avoid
anything looking at the limits getting confused.
(Although maybe that doesn't matter here?)

	David

> 
> Thanks,
> Michal