Re: [PATCH] PCI: Move test of INTx masking to pci_setup_device

[Alex Williamson]

On Thu, 25 May 2017 21:22:01 +0300
"Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:

> On Thu, May 25, 2017 at 07:13:23PM +0100, Piotr Gregor wrote:
> > The test for INTx masking via config space command performed
> > in pci_intx_mask_supported should be performed before PCI device
> > can be used. This is to avoid reading/writing of PCI_COMMAND_INTX_DISABLE
> > register which may collide with MSI/MSI-X interrupts.
> > 
> > This patch simplifies test performed in pci_intx_mask_supported
> > and introduces intx_mask_support field in struct pci_dev to store
> > the result. The test itself is moved to pci_setup_device.
> > The result can be queried at any time later from the pci_dev with
> > 
> > static inline bool pci_is_intx_mask_supported(struct pci_dev *pdev)
> > {
> >         /*
> >          * INTx masking is supported if device passed INTx test
> >          * and it's INTx masking feature works properly.
> >          */
> >         return (pdev->intx_mask_support && !pdev->broken_intx_masking);
> > }
> > 
> > Signed-off-by: Piotr Gregor <piotrgregor@xxxxxxxxxxx>
> > ---
> >  drivers/pci/pci.c             | 42 +++++++++++++++++++++++-------------------
> >  drivers/pci/probe.c           |  3 +++
> >  drivers/uio/uio_pci_generic.c |  2 +-
> >  drivers/vfio/pci/vfio_pci.c   |  2 +-
> >  include/linux/pci.h           | 10 ++++++++++
> >  5 files changed, 38 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index b01bd5b..bcaab9b 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -3709,42 +3709,46 @@ void pci_intx(struct pci_dev *pdev, int enable)
> >  EXPORT_SYMBOL_GPL(pci_intx);
> >  
> >  /**
> > - * pci_intx_mask_supported - probe for INTx masking support
> > + * pci_intx_mask_supported - probe for INTx masking support in pci_setup_device
> >   * @dev: the PCI device to operate on
> >   *
> > - * Check if the device dev support INTx masking via the config space
> > - * command word.
> > + * Check if the device dev supports INTx masking via the config space
> > + * command word. Executed when PCI device is setup. Result is saved
> > + * in intx_mask_support field of pci_dev and should be checked
> > + * with pci_is_intx_mask_supported() after PCI device has been setup
> > + * to avoid reading/writing of PCI_COMMAND_INTX_DISABLE register.
> >   */
> >  bool pci_intx_mask_supported(struct pci_dev *dev)
> >  {
> > -	bool mask_supported = false;
> > -	u16 orig, new;
> > +	u16 orig, toggle, new;
> >  
> > +	/*
> > +	 * If device doesn't support this feature though it could pass the test.
> > +	 */
> >  	if (dev->broken_intx_masking)
> >  		return false;
> >  
> >  	pci_cfg_access_lock(dev);
> >  
> > +	/*
> > +	 * Perform the test.
> > +	 */
> >  	pci_read_config_word(dev, PCI_COMMAND, &orig);
> > -	pci_write_config_word(dev, PCI_COMMAND,
> > -			      orig ^ PCI_COMMAND_INTX_DISABLE);
> > +	toggle = orig ^ PCI_COMMAND_INTX_DISABLE;
> > +	pci_write_config_word(dev, PCI_COMMAND, toggle);
> >  	pci_read_config_word(dev, PCI_COMMAND, &new);
> >  
> >  	/*
> > -	 * There's no way to protect against hardware bugs or detect them
> > -	 * reliably, but as long as we know what the value should be, let's
> > -	 * go ahead and check it.
> > +	 * Restore initial state.
> >  	 */
> > -	if ((new ^ orig) & ~PCI_COMMAND_INTX_DISABLE) {
> > -		dev_err(&dev->dev, "Command register changed from 0x%x to 0x%x: driver or hardware bug?\n",
> > -			orig, new);
> > -	} else if ((new ^ orig) & PCI_COMMAND_INTX_DISABLE) {
> > -		mask_supported = true;
> > -		pci_write_config_word(dev, PCI_COMMAND, orig);
> > -	}
> > +	pci_write_config_word(dev, PCI_COMMAND, orig);
> >  
> >  	pci_cfg_access_unlock(dev);
> > -	return mask_supported;
> > +
> > +	if (new == toggle)
> > +		return true;
> > +
> > +	return false;
> >  }
> >  EXPORT_SYMBOL_GPL(pci_intx_mask_supported);
> >  
> > @@ -3798,7 +3802,7 @@ static bool pci_check_and_set_intx_mask(struct pci_dev *dev, bool mask)
> >   * @dev: the PCI device to operate on
> >   *
> >   * Check if the device dev has its INTx line asserted, mask it and
> > - * return true in that case. False is returned if not interrupt was
> > + * return true in that case. False is returned if no interrupt was
> >   * pending.
> >   */
> >  bool pci_check_and_mask_intx(struct pci_dev *dev)
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 19c8950..16c60ce 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -1399,6 +1399,9 @@ int pci_setup_device(struct pci_dev *dev)
> >  		}
> >  	}
> >  
> > +	if (pci_intx_mask_supported(dev))
> > +		dev->intx_mask_support = 1;
> > +
> >  	switch (dev->hdr_type) {		    /* header type */
> >  	case PCI_HEADER_TYPE_NORMAL:		    /* standard header */
> >  		if (class == PCI_CLASS_BRIDGE_PCI)
> > diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
> > index d0b508b..8cd443c 100644
> > --- a/drivers/uio/uio_pci_generic.c
> > +++ b/drivers/uio/uio_pci_generic.c
> > @@ -73,7 +73,7 @@ static int probe(struct pci_dev *pdev,
> >  		return -ENODEV;
> >  	}
> >  
> > -	if (!pci_intx_mask_supported(pdev)) {
> > +	if (!pci_is_intx_mask_supported(pdev)) {
> >  		err = -ENODEV;
> >  		goto err_verify;
> >  	}
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index 324c52e..933456e 100644
> > --- a/drivers/vfio/pci/vfio_pci.c
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -239,7 +239,7 @@ static int vfio_pci_enable(struct vfio_pci_device *vdev)
> >  			vdev->nointx = true;
> >  			pci_intx(pdev, 0);
> >  		} else
> > -			vdev->pci_2_3 = pci_intx_mask_supported(pdev);
> > +			vdev->pci_2_3 = pci_is_intx_mask_supported(pdev);
> >  	}
> >  
> >  	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 33c2b0b..0fbd278 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -367,6 +367,7 @@ struct pci_dev {
> >  	unsigned int    __aer_firmware_first_valid:1;
> >  	unsigned int	__aer_firmware_first:1;
> >  	unsigned int	broken_intx_masking:1;
> > +	unsigned int	intx_mask_support:1;	/* INTx masking is supported */
> >  	unsigned int	io_window_1k:1;	/* Intel P2P bridge 1K I/O windows */
> >  	unsigned int	irq_managed:1;
> >  	unsigned int	has_secondary_link:1;
> > @@ -1003,6 +1004,15 @@ int __must_check pci_reenable_device(struct pci_dev *);
> >  int __must_check pcim_enable_device(struct pci_dev *pdev);
> >  void pcim_pin_device(struct pci_dev *pdev);
> >  
> > +static inline bool pci_is_intx_mask_supported(struct pci_dev *pdev)
> > +{
> > +	/*
> > +	 * INTx masking is supported if device passed INTx test and it's INTx
> > +	 * masking feature works properly.
> > +	 */
> > +	return (pdev->intx_mask_support && !pdev->broken_intx_masking);
> > +}
> > +  
> 
> And now there's pci_is_intx_mask_supported and pci_intx_mask_supported
> which are the same except pci_intx_mask_supported shouldn't be called by
> anyone except in one place in pci code.
> 
> Pls don't do this. Rename pci_intx_mask_supported -> __pci_intx_mask_supported
> and then everyone can just keep calling pci_intx_mask_supported as previously,
> except it'll be faster and safer. And unexport
> __pci_intx_mask_supported.


I would additionally suggest not to have pci_dev.broken_intx_masking
and pci_dev.intx_masking_support.  Let's just use broken_intx_masking to
track either broken or unsupported.  Then pci_intx_mask_supported()
becomes simply "return !pdev->broken_intx_masking;".  Of course we skip
testing of devices that are already marked by quirks as broken.  Thanks,

Alex

> >  static inline int pci_is_enabled(struct pci_dev *pdev)
> >  {
> >  	return (atomic_read(&pdev->enable_cnt) > 0);
> > -- 
> > 2.1.4