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Message-ID: <20210621183724.GA3291108@bjorn-Precision-5520>
Date: Mon, 21 Jun 2021 13:37:24 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Amey Narkhede <ameynarkhede03@...il.com>
Cc: Shanker R Donthineni <sdonthineni@...dia.com>,
alex.williamson@...hat.com,
Raphael Norwitz <raphael.norwitz@...anix.com>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
kw@...ux.com, Sinan Kaya <okaya@...nel.org>,
Len Brown <lenb@...nel.org>,
"Rafael J . Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v7 2/8] PCI: Add new array for keeping track of ordering
of reset methods
On Mon, Jun 21, 2021 at 10:45:18PM +0530, Amey Narkhede wrote:
> On 21/06/21 10:02AM, Shanker R Donthineni wrote:
> > On 6/18/21 12:22 PM, Amey Narkhede wrote:
> > > I wonder if this would be easier if dev->reset_methods[] contained
> > > indices into pci_reset_fn_methods[], highest priority first, with the
> > > priority being determined when dev->reset_methods[] is updated. For
> > > example:
> > >
> > > const struct pci_reset_fn_method pci_reset_fn_methods[] = {
> > > { }, # 0
> > > { &pci_dev_specific_reset, .name = "device_specific" }, # 1
> > > { &pci_dev_acpi_reset, .name = "acpi" }, # 2
> > > { &pcie_reset_flr, .name = "flr" }, # 3
> > > { &pci_af_flr, .name = "af_flr" }, # 4
> > > { &pci_pm_reset, .name = "pm" }, # 5
> > > { &pci_reset_bus_function, .name = "bus" }, # 6
> > > };
> > >
> > > dev->reset_methods[] = [1, 2, 3, 4, 5, 6]
> > > means all reset methods are supported, in the default priority
> > > order
> > >
> > > dev->reset_methods[] = [1, 0, 0, 0, 0, 0]
> > > means only pci_dev_specific_reset is supported
> > >
> > > dev->reset_methods[] = [3, 5, 0, 0, 0, 0]
> > > means pcie_reset_flr and pci_pm_reset are supported, in that
> > > priority order
> >
> > What about keeping two bitmap fields 'resets_supported' and
> > 'resets_enabled' in pci_dev object and mange it through sysfs and
> > probe helper function. We can avoid two loops multiple paces and
> > takes only 2Bytes of memory to keep track resets.
> >
> > resets_supported ---> initialized during pci_dev setup
> > resets_enabled ---> Exposed to userspace through sysfs by default set to resets_supported
> >
> > include/linux/pci.h:
> > ------------------------
> > /* Different types of PCI resets possible, lower number is higher priority */
> > #define PCI_RESET_METHOD_DEVSPEC 0
> > #define PCI_RESET_METHOD_ACPI 1
> > #define PCI_RESET_METHOD_FLR 2
> > #define PCI_RESET_METHOD_Af_FLR 3
> > #define PCI_RESET_METHOD_PM 4
> > #define PCI_RESET_METHOD_BUS 5
> > #define PCI_RESET_METHOD_MAX 6
> >
> > struct pci_dev {
> > ...
> > u8 resets_supported;
> > u8 resets_enabled;
> > };
> >
> > static inline bool pci_reset_supported(struct pci_dev *dev)
> > {
> > return !!(dev->resets_supported);
> > }
> >
> >
> > drivers/pci/pci.c:
> > --------------------
> > const struct pci_reset_fn_method pci_reset_fn_methods[PCI_RESET_METHOD_MAX] = {
> > [PCI_RESET_METHOD_DEVSPEC] = { &pci_dev_specific_reset,
> > .name = "device_specific" },
> > [PCI_RESET_METHOD_ACPI] = { &pci_dev_acpi_reset, .name = "acpi" },
> > [PCI_RESET_METHOD_FLR] = { &pcie_reset_flr, .name = "flr" },
> > [PCI_RESET_METHOD_Af_FLR] = { &pci_af_flr, .name = "af_flr" },
> > [PCI_RESET_METHOD_PM] = { &pci_pm_reset, .name = "pm" },
> > [PCI_RESET_METHOD_BUS] = { &pci_reset_bus_function, .name = "bus" }
> > };
> >
> >
> > void pci_init_reset_methods(struct pci_dev *dev)
> > {
> > int i, rc;
> >
> > BUILD_BUG_ON(ARRAY_SIZE(pci_reset_fn_methods) != PCI_RESET_METHOD_MAX);
> > might_sleep();
> >
> > for (i = 0; i < PCI_RESET_METHOD_MAX; i++) {
> > rc = pci_reset_fn_methods[i].reset_fn(dev, PCI_RESET_PROBE);
> > if (!rc)
> > dev->resets_supported |= BIT(i);
> > else if (rc != -ENOTTY)
> > break;
> > }
> > dev->resets_enabled = dev->resets_supported;
> > }
> >
> > int __pci_reset_function_locked(struct pci_dev *dev)
> > {
> > int i, rc = -ENOTTY;
> >
> > might_sleep();
> >
> > for (i = 0; i < PCI_RESET_METHOD_MAX; i++) {
> > if (dev->resets_enabled & BIT(i)) {
> > rc = pci_reset_fn_methods[i].reset_fn(dev, 0);
> > if (rc != -ENOTTY)
> > return rc;
> > }
> > }
> >
> > if (rc == -ENOTTY)
> > pci_warn(dev, "No reset happened reason %s\n",
> > !!dev->resets_supported ?
> > "disabled by user" : "not supported");
> >
> > return rc;
> > }
> >
> > drivers/pci/pci-sysfs.c
> > ----------------------------
> > static ssize_t reset_method_store(struct device *dev,
> > struct device_attribute *attr,
> > const char *buf, size_t count)
> > {
> > struct pci_dev *pdev = to_pci_dev(dev);
> > u8 resets_enabled = 0;
> > ...
> > if (sysfs_streq(options, "default")) {
> > pdev->resets_enabled = pdev->resets_supported;
> > goto set_reset_methods;
> > }
> >
> > while ((name = strsep(&options, ",")) != NULL) {
> > if (sysfs_streq(name, ""))
> > continue;
> > name = strim(name);
> >
> > for (i = 0; i < PCI_RESET_METHOD_MAX; i++) {
> > if ((pdev->resets_supported & BIT(i)) &&
> > sysfs_streq(name, pci_reset_fn_methods[i].name)) {
> > resets_enabled |= BIT(i);
> > break;
> > }
> > }
> > ...
> > }
> >
> > set_reset_methods:
> > kfree(options);
> > pdev->resets_enabled = resets_enabled;
> > return count;
> > }
> >
> > static ssize_t reset_method_show(struct device *dev,
> > struct device_attribute *attr,
> > char *buf)
> > {
> > struct pci_dev *pdev = to_pci_dev(dev);
> > ssize_t len = 0;
> > int i;
> >
> > for (i = 0; i < PCI_RESET_METHOD_MAX; i++) {
> > if (pdev->resets_enabled & BIT(i))
> > len += sysfs_emit_at(buf, len, "%s%s",
> > len ? "," : "",
> > pci_reset_fn_methods[i].name);
> > }
> > len += sysfs_emit_at(buf, len, len ? "\n" : "");
> >
> > return len;
> > }
> >
> Thank you for the idea.
> Actually that would be coming full circle because Alex, Raphael and
> I tried similar approach earlier while prototyping for v2 but this
> implementation does look better than what I had at that time.
I thought part of the point of this series was to allow the user to
change the *order* of reset types. I don't think we can control the
ordering if we only keep a bit (or even two) per reset type.
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