Re: [PATCH] xen-pciback: provide a "reset" sysfs file to try harder at an SBR

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Jul 09, 2014 at 03:09:59PM +0100, David Vrabel wrote:
> The standard implementation of pci_reset_function() does not try an
> SBR if there are other sibling devices.  This is a common
> configuration for multi-function devices (e.g., GPUs with a HDMI audio
> device function).
> 
> If all the functions are co-assigned to the same domain at the same
> time, then it is safe to perform an SBR to reset all functions at the
> same time.

Is there a particular reason you don't want to lift some of the
code (see my pcistub_reset_pci_dev function in xen/pciback: Implement
PCI reset slot or bus with 'do_flr' SysFS attribute) to check
for this?

> 
> Add a "reset" sysfs file with the same interface as the standard one
> (i.e., write 1 to reset) that will try an SBR if all sibling devices
> are unbound or bound to pciback.
> 
> Note that this is weaker than the requirement for functions to be
> co-assigned, but the toolstack is expected to ensure this.
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
> Changes in v2:
> - defer creating sysfs node to late init.
> ---
>  drivers/xen/xen-pciback/pci_stub.c |  125 +++++++++++++++++++++++++++++++++++-
>  drivers/xen/xen-pciback/pciback.h  |    1 +
>  2 files changed, 123 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
> index d57a173..5697c2a 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -17,6 +17,7 @@
>  #include <linux/wait.h>
>  #include <linux/sched.h>
>  #include <linux/atomic.h>
> +#include <linux/delay.h>
>  #include <xen/events.h>
>  #include <asm/xen/pci.h>
>  #include <asm/xen/hypervisor.h>
> @@ -63,6 +64,117 @@ static LIST_HEAD(pcistub_devices);
>  static int initialize_devices;
>  static LIST_HEAD(seized_devices);
>  
> +/*
> + * pci_reset_function() will only work if there is a mechanism to
> + * reset that single function (e.g., FLR or a D-state transition).
> + * For PCI hardware that has two or more functions but no per-function
> + * reset, we can do a bus reset iff all the functions are co-assigned
> + * to the same domain.
> + *
> + * If a function has no per-function reset mechanism the 'reset' sysfs
> + * file that the toolstack uses to reset a function prior to assigning
> + * the device will be missing.  In this case, pciback adds its own
> + * which will try a bus reset.
> + *
> + * Note: pciback does not check for co-assigment before doing a bus
> + * reset, only that the devices are bound to pciback.  The toolstack
> + * is assumed to have done the right thing.
> + */
> +static int __pcistub_reset_function(struct pci_dev *dev)
> +{
> +	struct pci_dev *pdev;
> +	u16 ctrl;
> +	int ret;
> +
> +	ret = __pci_reset_function_locked(dev);
> +	if (ret == 0)
> +		return 0;
> +
> +	if (pci_is_root_bus(dev->bus) || dev->subordinate || !dev->bus->self)
> +		return -ENOTTY;
> +
> +	list_for_each_entry(pdev, &dev->bus->devices, bus_list) {
> +		if (pdev != dev && (!pdev->driver
> +				    || strcmp(pdev->driver->name, "pciback")))
> +			return -ENOTTY;
> +		pci_save_state(pdev);
> +	}
> +
> +	pci_read_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, &ctrl);
> +	ctrl |= PCI_BRIDGE_CTL_BUS_RESET;
> +	pci_write_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, ctrl);
> +	msleep(200);
> +
> +	ctrl &= ~PCI_BRIDGE_CTL_BUS_RESET;
> +	pci_write_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, ctrl);
> +	msleep(200);

Why not use pci_try_reset_slot(dev->slot) or pci_try_reset_bus(dev->bus)?

> +
> +	list_for_each_entry(pdev, &dev->bus->devices, bus_list)
> +		pci_restore_state(pdev);
> +
> +	return 0;
> +}
> +
> +static int pcistub_reset_function(struct pci_dev *dev)
> +{
> +	int ret;
> +
> +	device_lock(&dev->dev);
> +	ret = __pcistub_reset_function(dev);
> +	device_unlock(&dev->dev);
> +
> +	return ret;
> +}
> +
> +static ssize_t pcistub_reset_store(struct device *dev,
> +				   struct device_attribute *attr,
> +				   const char *buf, size_t count)
> +{
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +	unsigned long val;
> +	ssize_t result = strict_strtoul(buf, 0, &val);
> +
> +	if (result < 0)
> +		return result;
> +
> +	if (val != 1)
> +		return -EINVAL;
> +
> +	result = pcistub_reset_function(pdev);
> +	if (result < 0)
> +		return result;
> +	return count;
> +}
> +static DEVICE_ATTR(reset, 0200, NULL, pcistub_reset_store);
> +
> +static int pcistub_try_create_reset_file(struct pci_dev *pci)
> +{
> +	struct xen_pcibk_dev_data *dev_data = pci_get_drvdata(pci);
> +	struct device *dev = &pci->dev;
> +	struct kernfs_node *reset_dirent;
> +	int ret;
> +
> +	reset_dirent = sysfs_get_dirent(dev->kobj.sd, "reset");
> +	if (reset_dirent) {
> +		sysfs_put(reset_dirent);
> +		return 0;
> +	}
> +
> +	ret = device_create_file(dev, &dev_attr_reset);
> +	if (ret < 0)
> +		return ret;
> +	dev_data->created_reset_file = true;
> +	return 0;
> +}
> +
> +static void pcistub_remove_reset_file(struct pci_dev *pci)
> +{
> +	struct xen_pcibk_dev_data *dev_data = pci_get_drvdata(pci);
> +
> +	if (dev_data && dev_data->created_reset_file)
> +		device_remove_file(&pci->dev, &dev_attr_reset);
> +}
> +
>  static struct pcistub_device *pcistub_device_alloc(struct pci_dev *dev)
>  {
>  	struct pcistub_device *psdev;
> @@ -103,7 +215,8 @@ static void pcistub_device_release(struct kref *kref)
>  	/* Call the reset function which does not take lock as this
>  	 * is called from "unbind" which takes a device_lock mutex.
>  	 */
> -	__pci_reset_function_locked(dev);
> +	__pcistub_reset_function(psdev->dev);
> +
>  	if (pci_load_and_free_saved_state(dev, &dev_data->pci_saved_state))
>  		dev_dbg(&dev->dev, "Could not reload PCI state\n");
>  	else
> @@ -280,7 +393,7 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
>  	/* This is OK - we are running from workqueue context
>  	 * and want to inhibit the user from fiddling with 'reset'
>  	 */
> -	pci_reset_function(dev);
> +	pcistub_reset_function(dev);
>  	pci_restore_state(dev);
>  
>  	/* This disables the device. */
> @@ -404,7 +517,7 @@ static int pcistub_init_device(struct pci_dev *dev)
>  		dev_err(&dev->dev, "Could not store PCI conf saved state!\n");
>  	else {
>  		dev_dbg(&dev->dev, "resetting (FLR, D3, etc) the device\n");
> -		__pci_reset_function_locked(dev);
> +		__pcistub_reset_function(dev);
>  		pci_restore_state(dev);
>  	}
>  	/* Now disable the device (this also ensures some private device
> @@ -413,6 +526,10 @@ static int pcistub_init_device(struct pci_dev *dev)
>  	dev_dbg(&dev->dev, "reset device\n");
>  	xen_pcibk_reset_device(dev);
>  
> +	err = pcistub_try_create_reset_file(dev);
> +	if (err < 0)
> +		goto config_release;
> +
>  	dev->dev_flags |= PCI_DEV_FLAGS_ASSIGNED;
>  	return 0;
>  
> @@ -540,6 +657,8 @@ static void pcistub_remove(struct pci_dev *dev)
>  
>  	dev_dbg(&dev->dev, "removing\n");
>  
> +	pcistub_remove_reset_file(dev);
> +
>  	spin_lock_irqsave(&pcistub_devices_lock, flags);
>  
>  	xen_pcibk_config_quirk_release(dev);
> diff --git a/drivers/xen/xen-pciback/pciback.h b/drivers/xen/xen-pciback/pciback.h
> index f72af87..708ade9 100644
> --- a/drivers/xen/xen-pciback/pciback.h
> +++ b/drivers/xen/xen-pciback/pciback.h
> @@ -42,6 +42,7 @@ struct xen_pcibk_device {
>  struct xen_pcibk_dev_data {
>  	struct list_head config_fields;
>  	struct pci_saved_state *pci_saved_state;
> +	bool created_reset_file;
>  	unsigned int permissive:1;
>  	unsigned int warned_on_write:1;
>  	unsigned int enable_intx:1;
> -- 
> 1.7.10.4
>