linux-kernel - Re: [PATCH v2] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8

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Date: Tue, 19 Dec 2023 18:19:39 -0500
From: Esther Shimanovich <eshima@...gle.com>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Esther Shimanovich <eshimanovich@...omium.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Rajat Jain <rajatja@...gle.com>
Subject: Re: [PATCH v2] PCI: Relabel JHL6540 on Lenovo X1 Carbon 7,8

> Maybe use PCI_VENDOR_ID_LENOVO and move the check first - it is cheaper
> than string comparison. In general, symbolic constants are preferred to
> magic numbers.

That makes sense! Will do.

> Actually, do we really need to check DMI given the checks below?

I was advised by Rajat Jain to check DMI. This is the reasoning he
gave me: "I'm not certain if you can use subsystem vendor alone
because, subsystem vendor & ID are defined by the PCI device vendor I
think (Intel here). What if Intel sold the same bridges to another
company and has the same subsystem vendor / ID."
To me it seems like each company in practice has a different subsystem
ID, but I don't know enough to confirm this 100%. If you are confident
that the subsystem IDs are sufficient, let me know and I'm happy to
switch them.
I'd appreciate some more insight on this before I remove the DMI checks!

>
> > +
> > +     /* Not all 0x15d3 components are external facing */
> > +     if (dev->device == 0x15d3 &&
>
> Again, maybe PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_C_4C_BRIDGE?

Oh! I missed that. Will use, thanks!