linux-kernel - Re: [PATCH V3 1/2] PCI: add CRS support to error handling path

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Date:   Thu, 10 Nov 2016 13:39:45 -0500
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-pci@...r.kernel.org, timur@...eaurora.org,
        cov@...eaurora.org, alex.williamson@...hat.com,
        vikrams@...eaurora.org
Cc:     Lorenzo.Pieralisi@....com, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/2] PCI: add CRS support to error handling path

On 10/3/2016 1:36 AM, Sinan Kaya wrote:
> The PCIE spec allows an endpoint device to extend the initialization time
> beyond 1 second by issuing Configuration Request Retry Status (CRS) for a
> vendor ID read request.
> 
> This basically means "I'm busy now, please call me back later".
> 
> There are two moving parts to CRS support from the SW perspective. One part
> is to determine if CRS is supported or not. The second part is to set the
> CRS visibility register.
> 
> As part of the probe, the Linux kernel sets the above two conditions in
> pci_enable_crs function. The kernel is also honoring the returned CRS in
> pci_bus_read_dev_vendor_id function if supported. The function will poll up
> to specified amount of time while endpoint is returning CRS response.
> 
> The PCIe spec also allows CRS to be issued during cold, warm, hot and FLR
> resets.
> 
> The hot reset is initiated by starting a secondary bus reset. A bus/device
> restore follows the reset.  This patch is adding vendor ID read into dev
> restore function to validate that the device is accessible before writing
> the register contents. If the device issues CRS, the code might poll up
> to 60 seconds.
> 
> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> ---
>  drivers/pci/pci.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index aab9d51..c8749b9 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4020,6 +4020,12 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
>  
>  static void pci_dev_restore(struct pci_dev *dev)
>  {
> +	u32 l;
> +
> +	/* see if the device is accessible first */
> +	if (!pci_bus_read_dev_vendor_id(dev->bus, dev->devfn, &l, 60 * 1000))
> +		return;
> +
>  	pci_restore_state(dev);
>  	pci_reset_notify(dev, false);
>  }
> 

Any feedback on this direction?


-- 
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.