linux-kernel - Re: [PATCH v4 1/4] PCI: Clean up pci_scan

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Message-ID: <19ea2a8ff04c24708a6504924f7a91c1045308d0.camel@linux.ibm.com>
Date:   Fri, 22 Apr 2022 15:35:07 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-s390@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v4 1/4] PCI: Clean up pci_scan_slot()

On Fri, 2022-04-22 at 15:28 +0200, Niklas Schnelle wrote:
> While determining the next PCI function is factored out of
> pci_scan_slot() into next_fn() the former still handles the first
> function as a special case. This duplicates the code from the scan loop.
> 
> Furthermore the non ARI branch of next_fn() is generally hard to
> understand and especially the check for multifunction devices is hidden
> in the handling of NULL devices for non-contiguous multifunction. It
> also signals that no further functions need to be scanned by returning
> 0 via wraparound and this is a valid function number.
> 
> Improve upon this by transforming the conditions in next_fn() to be
> easier to understand.
> 
> By changing next_fn() to return -ENODEV instead of 0 when there is no
> next function we can then handle the initial function inside the loop
> and deduplicate the shared handling. This also makes it more explicit
> that only function 0 must exist.
> 
> No functional change is intended.
> 
> Cc: Jan Kiszka <jan.kiszka@...mens.com>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
>  drivers/pci/probe.c | 39 ++++++++++++++++++++-------------------
>  1 file changed, 20 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..2000e9858f12 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2579,8 +2579,7 @@ struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn)
>  }
>  EXPORT_SYMBOL(pci_scan_single_device);
>  
> -static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
> -			    unsigned int fn)
> +static int next_fn(struct pci_bus *bus, struct pci_dev *dev, int fn)
>  {
>  	int pos;
>  	u16 cap = 0;
> @@ -2588,24 +2587,27 @@ static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
>  
>  	if (pci_ari_enabled(bus)) {
>  		if (!dev)
> -			return 0;
> +			return -ENODEV;
> +
> 

Sorry the whitespace damage was of course not intended, fixed locally.


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