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PCI: Sleep rather than busy-wait for VPD access completion 

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>
hifive-unleashed-5.1
Bjorn Helgaas 2016-02-22 14:58:18 -06:00
parent 408641e93a
commit c521b014cd
1 changed files with 10 additions and 8 deletions
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18
drivers/pci/access.c
View File

@ -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,