netdev - Re: [PATCH net-next v2 5/6] bnxt_en: Skip reading PXP registers during ethtool -d if unsupported

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Message-ID: <20241219065953.73e08f77@kernel.org>
Date: Thu, 19 Dec 2024 06:59:53 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Michael Chan <michael.chan@...adcom.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, andrew+netdev@...n.ch, pavan.chebbi@...adcom.com,
 andrew.gospodarek@...adcom.com, Ajit Khaparde <ajit.khaparde@...adcom.com>,
 Kalesh AP <kalesh-anakkur.purayil@...adcom.com>, Somnath Kotur
 <somnath.kotur@...adcom.com>
Subject: Re: [PATCH net-next v2 5/6] bnxt_en: Skip reading PXP registers
 during ethtool -d if unsupported

On Wed, 18 Dec 2024 22:57:09 -0800 Michael Chan wrote:
> > On Tue, 17 Dec 2024 10:26:19 -0800 Michael Chan wrote:  
> > > Newer firmware does not allow reading the PXP registers during
> > > ethtool -d, so skip the firmware call in that case.  Userspace
> > > (bnxt.c) always expects the register block to be populated so
> > > zeroes will be returned instead.  
> >
> > We have both the ability to return the number of registers (regs_len),
> > and the regs->version. Are you sure you don't want to use either option
> > to let user space know the regs aren't there?  
> 
> The existing bnxt.c in userspace since 2020 always assumes that the
> beginning part always contains the PXP register block regardless of
> regs->version as long as the register length >= the length of the
> register block.  I guess we didn't anticipate that this PXP block
> would ever be changed or FW would disallow reading it.

So if you bumped the version the existing userspace wouldn't care but
then you _could_ follow up and update user space to ignore these
registers when version is 1?

It's alright, it's just debug, I got curious recently about how little
use the version field gets. I'm not sure anyone has a good idea on
what to do with it.