linux-kernel - Re: [PATCH v11 1/4] PCI: Don't ignore valid response before CRS timeout

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Message-ID: <20170821174447.GA28977@bhelgaas-glaptop.roam.corp.google.com>
Date:   Mon, 21 Aug 2017 12:44:47 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Timur Tabi <timur@...eaurora.org>,
        linux-kernel@...r.kernel.org,
        Alex Williamson <alex.williamson@...hat.com>,
        linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v11 1/4] PCI: Don't ignore valid response before CRS
 timeout

On Mon, Aug 21, 2017 at 10:02:55AM -0400, Sinan Kaya wrote:
> On 8/18/2017 5:32 PM, Bjorn Helgaas wrote:
> > While waiting for a device to become ready (i.e., to return a non-CRS
> > completion to a read of its Vendor ID), if we got a valid response to the
> > very last read before timing out, we printed a warning and gave up on the
> > device even though it was actually ready.
> > 
> > For a typical 60s timeout, we wait about 65s (it's not exact because of the
> > exponential backoff), but we treated devices that became ready between 33s
> > and 65s as though they failed.
> > 
> > Move the Device ID read later so we check whether the device is ready
> > immediately, before checking for a timeout.
> > 
> > Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> > ---
> >  drivers/pci/probe.c |    7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index c31310db0404..08ea844ac4ba 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -1849,15 +1849,16 @@ bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *l,
> >  
> >  		msleep(delay);
> >  		delay *= 2;
> > -		if (pci_bus_read_config_dword(bus, devfn, PCI_VENDOR_ID, l))
> > -			return false;
> > -		/* Card hasn't responded in 60 seconds?  Must be stuck. */
> > +
> 
> There is still a problem here. We'll wait some time above and return without checking if
> we actually found the card or not.
> 
> >  		if (delay > crs_timeout) {
> >  			printk(KERN_WARNING "pci %04x:%02x:%02x.%d: not responding\n",
> >  			       pci_domain_nr(bus), bus->number, PCI_SLOT(devfn),
> >  			       PCI_FUNC(devfn));
> >  			return false;
> >  		}
> > +
> > +		if (pci_bus_read_config_dword(bus, devfn, PCI_VENDOR_ID, l))
> > +			return false;
> >  	}
> >  
> >  	return true;
> > 
> > 
> 
> Here is another shot at it. Sorry, I don't have a diff syntax. I made up the function
> by copy paste.

Yep, this is much better, thanks!

> 	while ((*l & 0xffff) == 0x0001) {
> 		if (!crs_timeout)
> 			return false;
>  
> 		/* Card hasn't responded in 60 seconds?  Must be stuck. */
> 		if (delay > crs_timeout) {
> 			printk(KERN_WARNING "pci %04x:%02x:%02x.%d: not responding\n",
> 			       pci_domain_nr(bus), bus->number, PCI_SLOT(devfn),
> 			       PCI_FUNC(devfn));
> 			return false;
> 		} 
> 		msleep(delay);
> 		delay *= 2;
> 		if (pci_bus_read_config_dword(bus, devfn, PCI_VENDOR_ID, l))
> 			return false; 
> 	}
> 
> -- 
> Sinan Kaya
> Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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