Re: [PATCH] PCI: Add CRS timeout for pci_device_is_present()

[Thierry Reding <treding@nvidia.com>]

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On Sat, Oct 05, 2019 at 11:51:29PM +0530, Vidya Sagar wrote:
> Adds a 60 seconds timeout to consider CRS (Configuration request Retry
> Status) from a downstream device when Vendor ID read is attempted by
> an upstream device. This helps to work with devices that return CRS
> during system resume. This also makes pci_device_is_present() consistent
> with the probe path where 60 seconds timeout is already being used.
> 
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
>  drivers/pci/pci.c   | 3 ++-
>  drivers/pci/pci.h   | 2 ++
>  drivers/pci/probe.c | 2 +-
>  3 files changed, 5 insertions(+), 2 deletions(-)

I think this makes sense, so:

Reviewed-by: Thierry Reding <treding@nvidia.com>

However, it looks like Sinan has researched this extensively in the past
and gave a presentation on this at Plumbers in 2017:

	https://blog.linuxplumbersconf.org/2017/ocw/system/presentations/4732/original/crs.pdf

Adding Sinan to see if he has any concerns about this, since resume time
is explicitly mentioned in the above slides.

Thierry

> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 95dc78ebdded..3ab9f6d3c8a6 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5905,7 +5905,8 @@ bool pci_device_is_present(struct pci_dev *pdev)
>  
>  	if (pci_dev_is_disconnected(pdev))
>  		return false;
> -	return pci_bus_read_dev_vendor_id(pdev->bus, pdev->devfn, &v, 0);
> +	return pci_bus_read_dev_vendor_id(pdev->bus, pdev->devfn, &v,
> +					  PCI_CRS_TIMEOUT);
>  }
>  EXPORT_SYMBOL_GPL(pci_device_is_present);
>  
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 3f6947ee3324..aa25c5fdc6a5 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -4,6 +4,8 @@
>  
>  #include <linux/pci.h>
>  
> +#define PCI_CRS_TIMEOUT		(60 * 1000)	/* 60 sec*/
> +
>  #define PCI_FIND_CAP_TTL	48
>  
>  #define PCI_VSEC_ID_INTEL_TBT	0x1234	/* Thunderbolt */
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 7c5d68b807ef..6e44a03283c8 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2258,7 +2258,7 @@ static struct pci_dev *pci_scan_device(struct pci_bus *bus, int devfn)
>  	struct pci_dev *dev;
>  	u32 l;
>  
> -	if (!pci_bus_read_dev_vendor_id(bus, devfn, &l, 60*1000))
> +	if (!pci_bus_read_dev_vendor_id(bus, devfn, &l, PCI_CRS_TIMEOUT))
>  		return NULL;
>  
>  	dev = pci_alloc_dev(bus);
> -- 
> 2.17.1
> 

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