RE: [PATCH] net/nfp: support 48-bit DMA address for firmware with NFDk

[Chaoyong He <chaoyong.he@corigine.com>]

> -----Original Message-----
> From: Niklas Soderlund <niklas.soderlund@corigine.com>
> Sent: Thursday, February 16, 2023 6:37 PM
> To: Kevin Traynor <ktraynor@redhat.com>
> Cc: Ferruh Yigit <ferruh.yigit@amd.com>; Xueming(Steven) Li
> <xuemingl@nvidia.com>; Chaoyong He <chaoyong.he@corigine.com>;
> dev@dpdk.org; Luca Boccassi <bluca@debian.org>; oss-drivers <oss-
> drivers@corigine.com>; Nole Zhang <peng.zhang@corigine.com>; Kevin Liu
> <jin.liu@corigine.com>; stable@dpdk.org
> Subject: Re: [PATCH] net/nfp: support 48-bit DMA address for firmware with
> NFDk
> 
> Hi Kevin,
> 
> Thanks for your input.
> 
> On 2023-02-16 10:28:34 +0000, Kevin Traynor wrote:
> > On 15/02/2023 18:28, Ferruh Yigit wrote:
> > > On 2/15/2023 5:47 PM, Niklas Söderlund wrote:
> > > > Hi Ferruh,
> > > >
> > > > Thanks for your continues effort in dealing with NFP patches.
> > > >
> > > > On 2023-02-15 13:42:01 +0000, Ferruh Yigit wrote:
> > > > > On 2/8/2023 9:15 AM, Chaoyong He wrote:
> > > > > > From: Peng Zhang <peng.zhang@corigine.com>
> > > > > >
> > > > > > 48-bit DMA address is supported in the firmware with NFDk, so
> > > > > > enable this feature in PMD now. But the firmware with NFD3
> > > > > > still just support 40-bit DMA address.
> > > > > >
> > > > > > RX free list descriptor, used by both NFD3 and NFDk, is also
> > > > > > modified to support 48-bit DMA address. That's OK because the
> > > > > > top bits is always set to 0 when assigned with 40-bit DMA address.
> > > > > >
> > > > > > Fixes: c73dced48c8c ("net/nfp: add NFDk Tx")
> > > > > > Cc: jin.liu@corigine.com
> > > > > > Cc: stable@dpdk.org
> > > > > >
> > > > >
> > > > > Why a backport is requested? As far as I understand this is not
> > > > > fixing anything but extending device capability. Is this a fix?
> > > >
> > > > I agree this is a bit of a grey zone. We reasoned this was a fix
> > > > as we should have done this from the start in the commit that
> > > > added support for NFDk. Are you OK moving forward with this as a
> > > > fix or would you prefer we resubmit without the request to backport?
> > > >
> > >
> > > I am not sure, is this change have any potential to change behavior
> > > for existing users?
> > > Like if one of your user is using 22.11.1 release, and if this patch
> > > backported to next LTS version, 22.11.2, will user notice any difference?
> > >
> > >
> > > @Luca, @Kevin, what is your comment as LTS maintainers?
> > >
> >
> > A bit difficult to know. If NFDk is not practicably usable without it,
> > then it could be considered a fix. If it's just extending to add
> > nice-to-have functionality then probably it is not a fix.
> 
> I think we can treat this as a nice-to-have and not something that makes
> NFDk unusable. As stated above, we marked this as a Fix as we *really*
> should have done this in the commit which added NFDk support.
> 
> @Ferruh, would you prefer we send a v2 or will you drop the Fixes and CC
> tags when/if applying?
> 

Actually, the DPDK app using the nfp card with a firmware of NFDk will coredump without this patch.
And that's the directly reason we consider backport this patch.

> >
> > It would need to ensure that it is tested on 22.11 branch and there
> > are no regressions. It is only relevant to DPDK 22.11 LTS so Cc
> > Xueming who will ultimately decide.
> >
> > A guide below on some things to consider for this type of backport is here:
> > http://doc.dpdk.org/guides/contributing/stable.html#what-changes-shoul
> > d-be-backported
> >
> > > > >
> > > > > > Signed-off-by: Peng Zhang <peng.zhang@corigine.com>
> > > > > > Reviewed-by: Chaoyong He <chaoyong.he@corigine.com>
> > > > > > Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
> > > > >
> > > >
> > >
> >
> 
> --
> Kind Regards,
> Niklas Söderlund