Re: [PATCH v7 1/8] PCI: Add pcie_reset_flr to follow calling convention of other reset methods

[Alex Williamson]

On Thu, 17 Jun 2021 16:57:34 -0500
Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:

> [+cc Christoph, since he added pcie_flr()]
> 
> On Tue, Jun 08, 2021 at 11:18:50AM +0530, Amey Narkhede wrote:
> > Currently there is separate function pcie_has_flr() to probe if pcie flr is
> > supported by the device which does not match the calling convention
> > followed by reset methods which use second function argument to decide
> > whether to probe or not.  Add new function pcie_reset_flr() that follows
> > the calling convention of reset methods.  
> 
> I don't like the fact that we handle FLR differently from other types
> of reset, so I do like the fact that this makes them more consistent.
> 
> > Reviewed-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Reviewed-by: Raphael Norwitz <raphael.norwitz@xxxxxxxxxxx>
> > Co-developed-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Signed-off-by: Amey Narkhede <ameynarkhede03@xxxxxxxxx>
> > ---
> >  drivers/crypto/cavium/nitrox/nitrox_main.c |  4 +-
> >  drivers/pci/pci.c                          | 62 ++++++++++++----------
> >  drivers/pci/pcie/aer.c                     | 12 ++---
> >  drivers/pci/quirks.c                       |  9 ++--
> >  include/linux/pci.h                        |  2 +-
> >  5 files changed, 43 insertions(+), 46 deletions(-)
> > 
> > diff --git a/drivers/crypto/cavium/nitrox/nitrox_main.c b/drivers/crypto/cavium/nitrox/nitrox_main.c
> > index facc8e6bc..15d6c8452 100644
> > --- a/drivers/crypto/cavium/nitrox/nitrox_main.c
> > +++ b/drivers/crypto/cavium/nitrox/nitrox_main.c
> > @@ -306,9 +306,7 @@ static int nitrox_device_flr(struct pci_dev *pdev)
> >  		return -ENOMEM;
> >  	}
> >  
> > -	/* check flr support */
> > -	if (pcie_has_flr(pdev))
> > -		pcie_flr(pdev);
> > +	pcie_reset_flr(pdev, 0);
> >  
> >  	pci_restore_state(pdev);
> >  
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 452351025..3bf36924c 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -4611,32 +4611,12 @@ int pci_wait_for_pending_transaction(struct pci_dev *dev)
> >  }
> >  EXPORT_SYMBOL(pci_wait_for_pending_transaction);
> >  
> > -/**
> > - * pcie_has_flr - check if a device supports function level resets
> > - * @dev: device to check
> > - *
> > - * Returns true if the device advertises support for PCIe function level
> > - * resets.
> > - */
> > -bool pcie_has_flr(struct pci_dev *dev)
> > -{
> > -	u32 cap;
> > -
> > -	if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET)
> > -		return false;
> > -
> > -	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &cap);
> > -	return cap & PCI_EXP_DEVCAP_FLR;
> > -}
> > -EXPORT_SYMBOL_GPL(pcie_has_flr);
> > -
> >  /**
> >   * pcie_flr - initiate a PCIe function level reset
> >   * @dev: device to reset
> >   *
> > - * Initiate a function level reset on @dev.  The caller should ensure the
> > - * device supports FLR before calling this function, e.g. by using the
> > - * pcie_has_flr() helper.
> > + * Initiate a function level reset unconditionally on @dev without
> > + * checking any flags and DEVCAP
> >   */
> >  int pcie_flr(struct pci_dev *dev)
> >  {
> > @@ -4659,6 +4639,31 @@ int pcie_flr(struct pci_dev *dev)
> >  }
> >  EXPORT_SYMBOL_GPL(pcie_flr);
> >  
> > +/**
> > + * pcie_reset_flr - initiate a PCIe function level reset
> > + * @dev: device to reset
> > + * @probe: If set, only check if the device can be reset this way.
> > + *
> > + * Initiate a function level reset on @dev.
> > + */
> > +int pcie_reset_flr(struct pci_dev *dev, int probe)
> > +{
> > +	u32 cap;
> > +
> > +	if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET)
> > +		return -ENOTTY;
> > +
> > +	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &cap);
> > +	if (!(cap & PCI_EXP_DEVCAP_FLR))
> > +		return -ENOTTY;
> > +
> > +	if (probe)
> > +		return 0;
> > +
> > +	return pcie_flr(dev);  
> 
> Christoph added pcie_flr() with a60a2b73ba69 ("PCI: Export
> pcie_flr()"), where the commit log says he split out the probing
> because "non-core callers already know their hardware."
> 
> It *is* reasonable to expect that drivers know whether their device
> supports FLR so they don't need to probe.

I don't think it changes your suggestion below, but this statement is a
little troublesome when we look at devices running in VMs where we've
been known to hide various capabilities, or simply quirks where some
combination of a known device feature might be otherwise avoided.  A
more robust driver should try to make fewer assumptions for these
cases, if not simply the inability to predict future changes to the
hardware.  

FLR should be a relatively rare event, but caching for driver API
purposes seems reasonable.  Thanks,

Alex

> But we don't expose the "probe" argument outside the PCI core for any
> other reset methods, and I would like to avoid that here.
> 
> It seems excessive to have to read PCI_EXP_DEVCAP every time.
> PCI_EXP_DEVCAP_FLR is a read-only bit, and we should only need to look
> at it once.
> 
> What I would really like here is a single bit in the pci_dev that we
> could set at enumeration-time, e.g., something like this:
> 
>   struct pci_dev {
>     ...
>     unsigned int has_flr:1;
>   };
> 
>   void set_pcie_port_type(...)    # during enumeration
>   {
>     pci_read_config_word(dev, pos + PCI_EXP_DEVCAP, &reg16);
>     if (reg16 & PCI_EXP_DEVCAP_FLR)
>       dev->has_flr = 1;
>   }
> 
>   static void quirk_no_flr(...)
>   {
>     dev->has_flr = 0;             # get rid of PCI_DEV_FLAGS_NO_FLR_RESET
>   }
> 
>   int pcie_flr(...)
>   {
>     if (!dev->has_flr)
>       return -ENOTTY;
> 
>     if (!pci_wait_for_pending_transaction(dev))
>       ...
>   }
> 
> I think this should be enough that we could get rid of pcie_has_flr()
> without having to expose the "probe" argument outside drivers/pci/.
> 
> Procedural note: if we *do* have to expose the "probe" argument, can
> you arrange it to have the correct type before touching the drivers, so
> we only have to touch the drivers once?
> 
> > +}
> > +EXPORT_SYMBOL_GPL(pcie_reset_flr);
> > +
> >  static int pci_af_flr(struct pci_dev *dev, int probe)
> >  {
> >  	int pos;
> > @@ -5139,11 +5144,9 @@ int __pci_reset_function_locked(struct pci_dev *dev)
> >  	rc = pci_dev_specific_reset(dev, 0);
> >  	if (rc != -ENOTTY)
> >  		return rc;
> > -	if (pcie_has_flr(dev)) {
> > -		rc = pcie_flr(dev);
> > -		if (rc != -ENOTTY)
> > -			return rc;
> > -	}
> > +	rc = pcie_reset_flr(dev, 0);
> > +	if (rc != -ENOTTY)
> > +		return rc;
> >  	rc = pci_af_flr(dev, 0);
> >  	if (rc != -ENOTTY)
> >  		return rc;
> > @@ -5174,8 +5177,9 @@ int pci_probe_reset_function(struct pci_dev *dev)
> >  	rc = pci_dev_specific_reset(dev, 1);
> >  	if (rc != -ENOTTY)
> >  		return rc;
> > -	if (pcie_has_flr(dev))
> > -		return 0;
> > +	rc = pcie_reset_flr(dev, 1);
> > +	if (rc != -ENOTTY)
> > +		return rc;
> >  	rc = pci_af_flr(dev, 1);
> >  	if (rc != -ENOTTY)
> >  		return rc;
> > diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> > index ec943cee5..98077595a 100644
> > --- a/drivers/pci/pcie/aer.c
> > +++ b/drivers/pci/pcie/aer.c
> > @@ -1405,13 +1405,11 @@ static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
> >  	}
> >  
> >  	if (type == PCI_EXP_TYPE_RC_EC || type == PCI_EXP_TYPE_RC_END) {
> > -		if (pcie_has_flr(dev)) {
> > -			rc = pcie_flr(dev);
> > -			pci_info(dev, "has been reset (%d)\n", rc);
> > -		} else {
> > -			pci_info(dev, "not reset (no FLR support)\n");
> > -			rc = -ENOTTY;
> > -		}
> > +		rc = pcie_reset_flr(dev, 0);
> > +		if (!rc)
> > +			pci_info(dev, "has been reset\n");
> > +		else
> > +			pci_info(dev, "not reset (no FLR support: %d)\n", rc);
> >  	} else {
> >  		rc = pci_bus_error_reset(dev);
> >  		pci_info(dev, "%s Port link has been reset (%d)\n",
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index d85914afe..f977ba79a 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -3819,7 +3819,7 @@ static int nvme_disable_and_flr(struct pci_dev *dev, int probe)
> >  	u32 cfg;
> >  
> >  	if (dev->class != PCI_CLASS_STORAGE_EXPRESS ||
> > -	    !pcie_has_flr(dev) || !pci_resource_start(dev, 0))
> > +	    pcie_reset_flr(dev, 1) || !pci_resource_start(dev, 0))
> >  		return -ENOTTY;
> >  
> >  	if (probe)
> > @@ -3888,13 +3888,10 @@ static int nvme_disable_and_flr(struct pci_dev *dev, int probe)
> >   */
> >  static int delay_250ms_after_flr(struct pci_dev *dev, int probe)
> >  {
> > -	if (!pcie_has_flr(dev))
> > -		return -ENOTTY;
> > +	int ret = pcie_reset_flr(dev, probe);
> >  
> >  	if (probe)
> > -		return 0;
> > -
> > -	pcie_flr(dev);
> > +		return ret;
> >  
> >  	msleep(250);
> >  
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index c20211e59..20b90c205 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -1225,7 +1225,7 @@ u32 pcie_bandwidth_available(struct pci_dev *dev, struct pci_dev **limiting_dev,
> >  			     enum pci_bus_speed *speed,
> >  			     enum pcie_link_width *width);
> >  void pcie_print_link_status(struct pci_dev *dev);
> > -bool pcie_has_flr(struct pci_dev *dev);
> > +int pcie_reset_flr(struct pci_dev *dev, int probe);
> >  int pcie_flr(struct pci_dev *dev);
> >  int __pci_reset_function_locked(struct pci_dev *dev);
> >  int pci_reset_function(struct pci_dev *dev);
> > -- 
> > 2.31.1
> >   
>