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Date:   Mon, 21 Jun 2021 22:45:18 +0530
From:   Amey Narkhede <ameynarkhede03@gmail.com>
To:     Shanker R Donthineni <sdonthineni@nvidia.com>
Cc:     Bjorn Helgaas <helgaas@kernel.org>, 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: <20210621171518.vs4h4y6ag2benlwp@archlinux>
References: <20210608054857.18963-3-ameynarkhede03@gmail.com>
 <20210617231305.GA3139128@bjorn-Precision-5520>
 <20210618172242.vs3qwimjpcicb4m4@archlinux>
 <1fb0a184-908c-5f98-ef6d-74edc602c2e0@nvidia.com>
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On 21/06/21 10:02AM, Shanker R Donthineni wrote:
> Hi Bjorn,
>
> 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.

Thanks,
Amey