From: Bjorn Helgaas <helgaas@kernel.org>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Amey Narkhede <ameynarkhede03@gmail.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Raphael Norwitz <raphael.norwitz@nutanix.com>,
linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
kw@linux.com, Shanker Donthineni <sdonthineni@nvidia.com>,
Sinan Kaya <okaya@kernel.org>, Len Brown <lenb@kernel.org>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>
Subject: Re: [PATCH v8 1/8] PCI: Add pcie_reset_flr to follow calling convention of other reset methods
Date: Fri, 2 Jul 2021 14:11:23 -0500 [thread overview]
Message-ID: <20210702191123.GA228462@bjorn-Precision-5520> (raw)
In-Reply-To: <20210630144955.71c5abac.alex.williamson@redhat.com>
Please add "()" after function names in subject lines.
On Wed, Jun 30, 2021 at 02:49:55PM -0600, Alex Williamson wrote:
> On Thu, 1 Jul 2021 01:34:15 +0530
> Amey Narkhede <ameynarkhede03@gmail.com> wrote:
> > On 21/06/30 11:56AM, Alex Williamson wrote:
> > > On Tue, 29 Jun 2021 21:30:57 +0530
> > > Amey Narkhede <ameynarkhede03@gmail.com> wrote:
> > >
> > > > Add has_flr bitfield in struct pci_dev to indicate support for pcie flr
> > > > to avoid reading PCI_EXP_DEVCAP multiple times and get rid of
> > > > PCI_DEV_FLAGS_NO_FLR_RESET in quirk_no_flr().
> > > >
> > > > 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.
s/pcie/PCIe/ (except for variables, function names, etc)
> > > > static int pci_af_flr(struct pci_dev *dev, int probe)
> > > > {
> > > > int pos;
> > > > u8 cap;
> > > >
> > > > - pos = pci_find_capability(dev, PCI_CAP_ID_AF);
> > > > - if (!pos)
> > > > + if (!dev->has_flr)
> > > > return -ENOTTY;
> > > >
> > > > - if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET)
> > > > + pos = pci_find_capability(dev, PCI_CAP_ID_AF);
> > > > + if (!pos)
> > > > return -ENOTTY;
> > > >
> > > > pci_read_config_byte(dev, pos + PCI_AF_CAP, &cap);
> > >
> > >
> > > How can has_flr encompass both methods of invoking FLR? PCIe FLR is
> > > not a prerequisite to AF FLR.
> > >
> > I see. Does this mean that there should be a separate flag for disabling
> > AF FLR?
>
> There hasn't been a need so far. Per the ECN, the AF capability is
> meant to make select PCIe features available on conventional PCI
> devices. It seems like it would be against the spirit of the AF
> capability to implement both an AF capability and a PCIe capability,
> but I don't see that it's definitively addressed by the spec.
>
> AF FLR is sufficiently rare that it's probably reasonable to make a
> has_pcie_flr bit on the device and leave AF FLR alone.
This sounds good to me. I agree that I'd prefer not to have a single
bit that applies to both AF FLR and PCIe FLR since they are distinct
mechanisms, discovered and initiated differently.
> I can't really say that I'm in favor of assigning a has_flr bit the
> double duty of also quirking broken FLR, if nothing else it's
> inconsistent with our other means of quirking resets.
By "other means of quirking resets," do you mean
PCI_DEV_FLAGS_NO_BUS_RESET, PCI_DEV_FLAGS_NO_PM_RESET, and
PCI_DEV_FLAGS_NO_FLR_RESET?
I agree that a pdev->has_pcie_flr bit would be different from those,
and maybe it's better to stick with PCI_DEV_FLAGS_NO_FLR_RESET for
now.
In general, I don't like the dual approach of some things being in the
pci_dev_flags enum and others being "unsigned int foo:1" in the struct
pci_dev because I can't tell if there's a reason to choose one over
the other. If there's not a reason to have both, I'd like to migrate
them all to the ":1" approach because it seems a little more readable
to me.
Bjorn
next prev parent reply other threads:[~2021-07-02 19:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-29 16:00 [PATCH v8 0/8] Expose and manage PCI device reset Amey Narkhede
2021-06-29 16:00 ` [PATCH v8 1/8] PCI: Add pcie_reset_flr to follow calling convention of other reset methods Amey Narkhede
2021-06-30 17:56 ` Alex Williamson
2021-06-30 20:04 ` Amey Narkhede
2021-06-30 20:49 ` Alex Williamson
2021-07-02 19:11 ` Bjorn Helgaas [this message]
2021-06-29 16:00 ` [PATCH v8 2/8] PCI: Add new array for keeping track of ordering of " Amey Narkhede
2021-06-30 18:33 ` Alex Williamson
2021-06-29 16:00 ` [PATCH v8 3/8] PCI: Remove reset_fn field from pci_dev Amey Narkhede
2021-06-29 16:01 ` [PATCH v8 4/8] PCI/sysfs: Allow userspace to query and set device reset mechanism Amey Narkhede
2021-06-30 18:49 ` Alex Williamson
2021-06-29 16:01 ` [PATCH v8 5/8] PCI: Define a function to set ACPI_COMPANION in pci_dev Amey Narkhede
2021-06-29 16:01 ` [PATCH v8 6/8] PCI: Setup ACPI fwnode early and at the same time with OF Amey Narkhede
2021-06-29 16:01 ` [PATCH v8 7/8] PCI: Add support for ACPI _RST reset method Amey Narkhede
2021-06-29 16:01 ` [PATCH v8 8/8] PCI: Change the type of probe argument in reset functions Amey Narkhede
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