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

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Message-ID: <f7127748-24cd-37bd-544a-8cba6bf5906d@codeaurora.org>
Date:   Mon, 21 Aug 2017 10:02:55 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     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 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.

	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.