PCI: Sleep rather than busy-wait for VPD access completion (c521b014) · Commits · 戴 / test

Use usleep_range() instead of udelay() while waiting for a VPD access to complete. This is not a performance path, so no need to hog the CPU. Rationale for usleep_range() parameters: We clear PCI_VPD_ADDR_F for a read (or set it for a write), then wait for the device to change it. For a device that updates PCI_VPD_ADDR between our config write and subsequent config read, we won't sleep at all and can get the device's maximum rate. Sleeping a minimum of 10 usec per 4-byte access limits throughput to about 400Kbytes/second. VPD is small (32K bytes at most), and most devices use only a fraction of that. We back off exponentially up to 1024 usec per iteration. If we reach 1024, we've already waited up to 1008 usec (16 + 32 + ... + 512), so if we miss an update and wait an extra 1024 usec, we can still get about 1/2 of the device's maximum rate. Tested-by:

Shane Seymour <shane.seymour@hpe.com> Tested-by:

Babu Moger <babu.moger@oracle.com> Signed-off-by:

Bjorn Helgaas <bhelgaas@google.com> Reviewed-by:

Hannes Reinecke <hare@suse.com>

drivers/pci/access.c

+10 −8

Original line number	Diff line number	Diff line
		@@ -342,14 +342,15 @@ static size_t pci_vpd_size(struct pci_dev *dev, size_t old_size)
		static int pci_vpd_wait(struct pci_dev *dev)
		{
		struct pci_vpd *vpd = dev->vpd;
		unsigned long timeout = jiffies + HZ/20 + 2;
		unsigned long timeout = jiffies + msecs_to_jiffies(50);
		unsigned long max_sleep = 16;
		u16 status;
		int ret;

		if (!vpd->busy)
		return 0;

		for (;;) {
		while (time_before(jiffies, timeout)) {
		ret = pci_user_read_config_word(dev, vpd->cap + PCI_VPD_ADDR,
		&status);
		if (ret < 0)
		@@ -360,15 +361,16 @@ static int pci_vpd_wait(struct pci_dev *dev)
		return 0;
		}

		if (time_after(jiffies, timeout)) {
		dev_printk(KERN_DEBUG, &dev->dev, "vpd r/w failed. This is likely a firmware bug on this device. Contact the card vendor for a firmware update\n");
		return -ETIMEDOUT;
		}
		if (fatal_signal_pending(current))
		return -EINTR;
		if (!cond_resched())
		udelay(10);

		usleep_range(10, max_sleep);
		if (max_sleep < 1024)
		max_sleep *= 2;
		}

		dev_warn(&dev->dev, "VPD access failed. This is likely a firmware bug on this device. Contact the card vendor for a firmware update\n");
		return -ETIMEDOUT;
		}

		static ssize_t pci_vpd_read(struct pci_dev *dev, loff_t pos, size_t count,

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