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Subject: Re: [PATCH v7 2/8] PCI: Add new array for keeping track of ordering
 of reset methods
To:     Amey Narkhede <ameynarkhede03@gmail.com>,
        Bjorn Helgaas <helgaas@kernel.org>
CC:     <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>
References: <20210608054857.18963-3-ameynarkhede03@gmail.com>
 <20210617231305.GA3139128@bjorn-Precision-5520>
 <20210618172242.vs3qwimjpcicb4m4@archlinux>
From:   Shanker R Donthineni <sdonthineni@nvidia.com>
Message-ID: <1fb0a184-908c-5f98-ef6d-74edc602c2e0@nvidia.com>
Date:   Mon, 21 Jun 2021 10:02:11 -0500
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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;
}