Re: [PATCH part1 v6 5/7] PCI: Add pci_dummy_ops to isolate pci device temporarily

[Gu Zheng]

Hi Yijing,
On 02/12/2014 10:52 AM, Yijing Wang wrote:

> Pci_dummy_ops does nothing when we use it to read/write
> pci_device. So we can isolate pci device by replace its
> bus pci_ops by pci_dummy_ops. This is preparation for
> the later patch.
> 
> Signed-off-by: Yijing Wang <wangyijing@xxxxxxxxxx>
> ---
>  drivers/pci/pci.c   |   62 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pci.h |    4 +++
>  2 files changed, 66 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index af34057..283e82e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2226,6 +2226,68 @@ bool pci_serial_number_changed(struct pci_dev *pdev)
>  }
>  EXPORT_SYMBOL(pci_serial_number_changed);
>  
> +static int pci_dummy_read(struct pci_bus *bus, unsigned int devfn,
> +		int where, int size, u32 *val)
> +{
> +	return PCIBIOS_DEVICE_NOT_FOUND;
> +}
> +
> +static int pci_dummy_write(struct pci_bus *bus, unsigned int devfn,
> +		int reg, int size, u32 val)
> +{
> +	return PCIBIOS_DEVICE_NOT_FOUND;
> +}
> +
> +static struct pci_ops pci_dummy_ops = {
> +	.read = pci_dummy_read,
> +	.write = pci_dummy_write,
> +};
> +
> +static DEFINE_SPINLOCK(pci_freeze_lock);
> +/**
> + * pci_bus_freeze_device - freeze pci bus to access pci device
> + * @bus: the pci bus to freeze
> + *
> + * Replace pci bus ops by pci_dummy_ops, protect system from
> + * accessing pci devices.
> + */
> +void pci_bus_freeze_device(struct pci_bus *bus)
> +{
> +	struct pci_ops *ops;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&pci_freeze_lock, flags);
> +	if (bus->is_frozen)
> +		goto out;
> +	bus->is_frozen = 1;
> +	ops = pci_bus_set_ops(bus, &pci_dummy_ops);
> +	bus->save_ops = ops;
> +out:
> +	spin_unlock_irqrestore(&pci_freeze_lock, flags);
> +}
> +
> +/**
> + * pci_bus_unfreeze_device - unfreeze pci bus to acess pci devices
> + * @bus: the pci bus to unfreeze
> + *
> + * Restore pci bus original ops, so pci bus can access
> + * pci devices normally.
> + */
> +void pci_bus_unfreeze_device(struct pci_bus *bus)
> +{
> +	unsigned long flags;
> +
> +	BUG_ON(!bus->save_ops);
> +	spin_lock_irqsave(&pci_freeze_lock, flags);
> +	if (!bus->is_frozen)
> +		goto out;

It seems that the BUG_ON() should placed here, otherwise it will be
triggered if we try to unfreeze the same bus multiply.

Regards,
Gu

> +	pci_bus_set_ops(bus, bus->save_ops);
> +	bus->save_ops = NULL;
> +	bus->is_frozen = 0;
> +out:
> +	spin_unlock_irqrestore(&pci_freeze_lock, flags);
> +}
> +
>  /**
>   * pci_configure_ari - enable or disable ARI forwarding
>   * @dev: the PCI device
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index d60c0b6..e3dd4ea 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -442,6 +442,7 @@ struct pci_bus {
>  	struct resource busn_res;	/* bus numbers routed to this bus */
>  
>  	struct pci_ops	*ops;		/* configuration access functions */
> +	struct pci_ops	*save_ops; /* save configuration access functions */
>  	struct msi_chip	*msi;		/* MSI controller */
>  	void		*sysdata;	/* hook for sys-specific extension */
>  	struct proc_dir_entry *procdir;	/* directory entry in /proc/bus/pci */
> @@ -460,6 +461,7 @@ struct pci_bus {
>  	struct bin_attribute	*legacy_io; /* legacy I/O for this bus */
>  	struct bin_attribute	*legacy_mem; /* legacy mem */
>  	unsigned int		is_added:1;
> +	unsigned int		is_frozen:1;
>  };
>  
>  #define pci_bus_b(n)	list_entry(n, struct pci_bus, node)
> @@ -1026,6 +1028,8 @@ ssize_t pci_read_vpd(struct pci_dev *dev, loff_t pos, size_t count, void *buf);
>  ssize_t pci_write_vpd(struct pci_dev *dev, loff_t pos, size_t count, const void *buf);
>  
>  bool pci_serial_number_changed(struct pci_dev *pdev);
> +void pci_bus_freeze_device(struct pci_bus *bus);
> +void pci_bus_unfreeze_device(struct pci_bus *bus);
>  
>  /* Helper functions for low-level code (drivers/pci/setup-[bus,res].c) */
>  resource_size_t pcibios_retrieve_fw_addr(struct pci_dev *dev, int idx);


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