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

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Message-ID: <ZYJFq6T3uGJVv0Nh@google.com>
Date: Tue, 19 Dec 2023 17:38:51 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Esther Shimanovich <eshima@...gle.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

On Tue, Dec 19, 2023 at 06:19:39PM -0500, Esther Shimanovich wrote:
> > 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."

I believe subsystem vendor and product IDs are not baked into the device
but set up by the system firmware, and therefore there should be no
concerns with mixing up IDs, but I am happy to be corrected by people
with more experience with PCI.

Thanks.

-- 
Dmitry