From: Bjorn Helgaas <helgaas@kernel.org>
To: Amey Narkhede <ameynarkhede03@gmail.com>,
Alex Williamson <alex.williamson@redhat.com>
Cc: 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 v7 1/8] PCI: Add pcie_reset_flr to follow calling convention of other reset methods
Date: Thu, 24 Jun 2021 11:15:59 -0500 [thread overview]
Message-ID: <20210624161559.GA3532867@bjorn-Precision-5520> (raw)
In-Reply-To: <20210624152809.m3glwh6lxckykt33@archlinux>
[+to Alex]
On Thu, Jun 24, 2021 at 08:58:09PM +0530, Amey Narkhede wrote:
> On 21/06/24 07:23AM, Bjorn Helgaas wrote:
> > 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.
> >
> > > +/**
> > > + * 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);
> > > +}
> >
> > Tangent: I've been told before, but I can't remember why we need the
> > "probe" interface. Since we're looking at this area again, can we add
> > a comment to clarify this?
> >
> > Every time I read this, I wonder why we can't just get rid of the
> > probe and attempt a reset. If it fails because it's not supported, we
> > could just try the next one in the list.
>
> Part of the reason is to have same calling convention as other reset
> methods and other reason is devices that run in VMs where various
> capabilities can be hidden or have quirks for avoiding known troublesome
> combination of device features as Alex explained here
> https://lore.kernel.org/linux-pci/20210624151242.ybew2z5rseuusj7v@archlinux/T/#mb67c09a2ce08ce4787652e4c0e7b9e5adf1df57a
>
> On the side note as you suggested earlier to cache flr capability
> earlier the PCI_EXP_DEVCAP reading code won't be there in next version
> so its just trivial check(dev->has_flr).
Sorry, I didn't make my question clear. I'm not asking why we're
adding a "probe" argument to pcie_reset_flr() to make it consistent
with pci_af_flr(), pci_pm_reset(), pci_parent_bus_reset(), etc. I
like making the interfaces consistent.
What I'm asking here is why the "probe" argument exists for *any* of
these interfaces and why pci_probe_reset_function() exists.
This is really more a question for Alex since it's a historical
question, not anything directly related to your series. I'm not
proposing *removing* the "probe" argument; I know it exists for a
reason because I've asked about it before. But I forgot the answer,
which makes me think a hint in the code would be useful.
Bjorn
next prev parent reply other threads:[~2021-06-24 16:16 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-08 5:48 [PATCH v7 0/8] Expose and manage PCI device reset Amey Narkhede
2021-06-08 5:48 ` [PATCH v7 1/8] PCI: Add pcie_reset_flr to follow calling convention of other reset methods Amey Narkhede
2021-06-10 20:15 ` Shanker R Donthineni
2021-06-17 21:57 ` Bjorn Helgaas
2021-06-17 22:51 ` Alex Williamson
2021-06-18 16:32 ` Amey Narkhede
2021-06-24 12:23 ` Bjorn Helgaas
2021-06-24 15:28 ` Amey Narkhede
2021-06-24 16:15 ` Bjorn Helgaas [this message]
2021-06-24 18:48 ` Alex Williamson
2021-06-08 5:48 ` [PATCH v7 2/8] PCI: Add new array for keeping track of ordering of " Amey Narkhede
2021-06-10 20:15 ` Shanker R Donthineni
2021-06-17 23:13 ` Bjorn Helgaas
2021-06-18 17:22 ` Amey Narkhede
2021-06-21 15:02 ` Shanker R Donthineni
2021-06-21 17:15 ` Amey Narkhede
2021-06-21 18:37 ` Bjorn Helgaas
2021-06-08 5:48 ` [PATCH v7 3/8] PCI: Remove reset_fn field from pci_dev Amey Narkhede
2021-06-10 20:16 ` Shanker R Donthineni
2021-06-08 5:48 ` [PATCH v7 4/8] PCI/sysfs: Allow userspace to query and set device reset mechanism Amey Narkhede
2021-06-09 21:57 ` Raphael Norwitz
2021-06-09 22:36 ` Shanker R Donthineni
2021-06-09 22:48 ` Raphael Norwitz
2021-06-10 20:16 ` Shanker R Donthineni
2021-06-18 20:00 ` Bjorn Helgaas
2021-06-19 13:59 ` Amey Narkhede
2021-06-21 13:01 ` Bjorn Helgaas
2021-06-21 17:28 ` Amey Narkhede
2021-06-21 19:07 ` Bjorn Helgaas
2021-06-21 19:33 ` Amey Narkhede
2021-06-23 12:06 ` Bjorn Helgaas
2021-06-23 14:07 ` Amey Narkhede
2021-06-23 17:56 ` Amey Narkhede
2021-06-23 17:21 ` Alex Williamson
2021-06-24 12:15 ` Bjorn Helgaas
2021-06-24 15:12 ` Amey Narkhede
2021-06-24 16:56 ` Bjorn Helgaas
2021-06-24 17:20 ` Shanker R Donthineni
2021-06-24 17:28 ` Amey Narkhede
2021-06-24 17:59 ` Bjorn Helgaas
2021-06-08 5:48 ` [PATCH v7 5/8] PCI: Setup ACPI_COMPANION early Amey Narkhede
2021-06-08 5:48 ` [PATCH v7 6/8] PCI: Add support for ACPI _RST reset method Amey Narkhede
2021-06-08 5:48 ` [PATCH v7 7/8] PCI: Enable NO_BUS_RESET quirk for Nvidia GPUs Amey Narkhede
2021-06-10 23:16 ` Bjorn Helgaas
2021-06-10 23:33 ` Shanker R Donthineni
2021-06-10 23:43 ` Shanker R Donthineni
2021-06-10 23:53 ` Bjorn Helgaas
2021-06-11 4:15 ` Shanker R Donthineni
2021-06-08 5:48 ` [PATCH v7 8/8] PCI: Change the type of probe argument in reset functions Amey Narkhede
2021-06-09 21:40 ` Raphael Norwitz
2021-06-08 10:05 ` [PATCH v7 0/8] Expose and manage PCI device reset Enrico Weigelt, metux IT consult
2021-06-08 15:44 ` Amey Narkhede
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