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Date:   Mon, 21 Jun 2021 13:37:24 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Amey Narkhede <ameynarkhede03@gmail.com>
Cc:     Shanker R Donthineni <sdonthineni@nvidia.com>,
        alex.williamson@redhat.com,
        Raphael Norwitz <raphael.norwitz@nutanix.com>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        kw@linux.com, Sinan Kaya <okaya@kernel.org>,
        Len Brown <lenb@kernel.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>
Subject: Re: [PATCH v7 2/8] PCI: Add new array for keeping track of ordering
 of reset methods
Message-ID: <20210621183724.GA3291108@bjorn-Precision-5520>
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In-Reply-To: <20210621171518.vs4h4y6ag2benlwp@archlinux>
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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.