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| author | Bjorn Helgaas <bhelgaas@google.com> | 2016-02-22 23:58:18 +0300 |
|---|---|---|
| committer | Bjorn Helgaas <bhelgaas@google.com> | 2016-03-10 23:24:48 +0300 |
| commit | c521b014cd51da94ae16c3decf1c407c3e0518f6 (patch) | |
| tree | 0671f6526a14de5aeb6991256b85f1cc1a001062 /drivers/pci/access.c | |
| parent | 408641e93aa5283e586fefd4dc72e67c92aae075 (diff) | |
| download | linux-c521b014cd51da94ae16c3decf1c407c3e0518f6.tar.xz | |
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>
Diffstat (limited to 'drivers/pci/access.c')
| -rw-r--r-- | drivers/pci/access.c | 18 |
1 files changed, 10 insertions, 8 deletions
diff --git a/drivers/pci/access.c b/drivers/pci/access.c index 8449d6b58178..01b9d0a00abc 100644 --- a/drivers/pci/access.c +++ b/drivers/pci/access.c @@ -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, |