Re: [dpdk-dev] [PATCH] bus/pci: nvme on Windows requires class id and bus

From: Tal Shnaiderman <talshn@nvidia.com>
To: Nick Connolly <nick.connolly@mayadata.io>,
	"dmitry.kozliuk@gmail.com" <dmitry.kozliuk@gmail.com>,
	"pallavi.kadam@intel.com" <pallavi.kadam@intel.com>,
	NBU-Contact-Thomas Monjalon <thomas@monjalon.net>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] bus/pci: nvme on Windows requires class id and bus
Date: Wed, 27 Jan 2021 15:13:35 +0000	[thread overview]
Message-ID: <DM6PR12MB39454497184512CC9C13C639A4BB9@DM6PR12MB3945.namprd12.prod.outlook.com> (raw)
In-Reply-To: <ee5d1820-e490-6e63-abe7-a1cca2117212@mayadata.io>

> Subject: Re: [PATCH] bus/pci: nvme on Windows requires class id and bus
> 
> External email: Use caution opening links or attachments
> 
> 
> Hi Tal,
> 
> Thanks for the comments.
> 
> >> +       /* Try and find PCI class ID */
> >> +       for (cp = buf; !(cp[0] == 0 && cp[1] == 0); cp++)
> > How about
> > for (cp = buf; cp[0] || cp[1]; cp++)
> That would be my preferred idiom, but the DPDK coding style (1.9.1) says 'do
> not use ! for tests unless it is a boolean' (but somewhat confusingly does so
> in a section on NULL pointers).  I interpreted it as a general prohibition on
> conditionals without an explicit operator (except for booleans).  I'd love to be
> corrected here!
> 
> >> +               if (*cp == '&' && sscanf_s(cp, "&CC_%" PRIx32,
> >> + &class_id) == 1)
> > Could there be a case where PCI\\VEN_v(4)&DEV_d(4)&CC_c(2)s(2) exist
> but PCI\\VEN_v(4)&DEV_d(4)&CC_c(2)s(2)p(2) doesn't? In that case the
> parsing would be incorrect.
> The MSDN documentation says that the most specific string will be returned
> first, in this case &CC_c(2)s(2)p(2), so if there is a 6-digit class ID we will
> return it.  That left me wondering what to do if we only encounter a 4-digit
> class ID.  If we ignore it, then we won't be able to match on the class ID.  We
> could parse it as 4-digits and supply zero for the p(2) field, but that left me
> wondering why Windows wouldn't have already done that for us.  What I see
> on my own systems is that there is always a 6-digit class ID defined, even if
> the pci-ids repository doesn't list any values for p(2) (e.g.
> https://pci-ids.ucw.cz/read/PD/07/80 reports as &CC_078000).
> 
> My conclusion was that was probably best just to return the first class ID that
> Windows reports even if it's only 4-digits.  That way the device can still be
> found and will match the CC_ info displayed in device manager.

I'd shift the class_id value to the right in case the returned value is 4 digit, just to verify the result would be "c(2)s(2) 0" and not "0 s(2)p(2)", however when testing your change I couldn't find a case where only 4 digits matched.

Either than that LGTM.
> 
> Thanks,
> Nick