netdev - Re: [PATCH net 1/3] nfp: use correct macro for LengthSelect in BAR config

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Message-ID: <ZcDvJ8fLWw7DCGZv@LouisNoVo>
Date: Mon, 5 Feb 2024 16:22:31 +0200
From: Louis Peens <louis.peens@...igine.com>
To: Simon Horman <horms@...nel.org>
Cc: David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	James Hershaw <james.hershaw@...igine.com>,
	Daniel Basilio <daniel.basilio@...igine.com>,
	netdev@...r.kernel.org, stable@...r.kernel.org,
	oss-drivers@...igine.com
Subject: Re: [PATCH net 1/3] nfp: use correct macro for LengthSelect in BAR
 config

On Mon, Feb 05, 2024 at 01:35:45PM +0000, Simon Horman wrote:
> On Fri, Feb 02, 2024 at 01:37:17PM +0200, Louis Peens wrote:
> > From: Daniel Basilio <daniel.basilio@...igine.com>
> > 
> > The 1st and 2nd expansion BAR configuration registers are configured,
> > when the driver starts up, in variables 'barcfg_msix_general' and
> > 'barcfg_msix_xpb', respectively. The 'LengthSelect' field is ORed in
> > from bit 0, which is incorrect. The 'LengthSelect' field should
> > start from bit 27.
> > 
> > This has largely gone un-noticed because
> > NFP_PCIE_BAR_PCIE2CPP_LengthSelect_32BIT happens to be 0.
> > 
> > Fixes: 4cb584e0ee7d ("nfp: add CPP access core")
> > Cc: stable@...r.kernel.org # 4.11+
> > Signed-off-by: Daniel Basilio <daniel.basilio@...igine.com>
> > Signed-off-by: Louis Peens <louis.peens@...igine.com>
> 
> Hi Daniel and Louis,
> 
> If I'm reading this right then this is a code-correctness issue
> and there is no runtime effect (because 0 is 0 regardless of shifting and
> masking).
You are reading this correctly yes.
> 
> If so, I'd suggest that this is net-next material.
> And, in turn, if so the Fixes tag should be dropped.
Thanks Simon. I was definitely flip-flopping on which tree to pick when
preparing this, if not already merged I would have gladly dropped it
from this net series. Thinking of it in terms of runtime effect is
probably a useful angle, will try and do this more when picking a tree.