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SubjectRe: [PATCH v7 1/8] PCI: Add pcie_reset_flr to follow calling convention of other reset methods
On Thu, 17 Jun 2021 16:57:34 -0500
Bjorn Helgaas <helgaas@kernel.org> 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@redhat.com>
> > Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> > Co-developed-by: Alex Williamson <alex.williamson@redhat.com>
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com>
> > ---
> > 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
> >
>

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