linux-kernel - Re: [PATCH v3 6/9] cxl/pci: Do not ignore PCI config read errors in match_add

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Date:   Wed, 9 Nov 2022 17:09:56 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Robert Richter <rrichter@....com>
Cc:     Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>
Subject: Re: [PATCH v3 6/9] cxl/pci: Do not ignore PCI config read errors in
 match_add_dports()

On Wed, Nov 09, 2022 at 11:40:56AM +0100, Robert Richter wrote:
> The link capabilities of a PCI device are read when enumerating its
> dports. This is done by reading the PCI config space. If that fails
> port enumeration ignores that error. However, reading the PCI config
> space should reliably work.
> 
> To reduce some complexity to the code flow when factoring out parts of
> the code in match_add_dports() for later reuse, change this to throw
> an error.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
>  drivers/cxl/core/pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index 0dbbe8d39b07..8271b8abde7a 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -47,7 +47,7 @@ static int match_add_dports(struct pci_dev *pdev, void *data)
>  		return 0;
>  	if (pci_read_config_dword(pdev, pci_pcie_cap(pdev) + PCI_EXP_LNKCAP,
>  				  &lnkcap))

You didn't change this, but I recommend using
pcie_capability_read_dword() when reading the PCIe Capability.  It
takes care of some annoying corner cases like devices that don't
implement Link Cap and the different versions of the PCIe Capability.

> -		return 0;
> +		return -ENXIO;
>  
>  	rc = cxl_find_regblock(pdev, CXL_REGLOC_RBI_COMPONENT, &map);
>  	if (rc)
> -- 
> 2.30.2
>