From c521b014cd51da94ae16c3decf1c407c3e0518f6 Mon Sep 17 00:00:00 2001 From: Bjorn Helgaas Date: Mon, 22 Feb 2016 14:58:18 -0600 Subject: [PATCH] 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 Tested-by: Babu Moger Signed-off-by: Bjorn Helgaas Reviewed-by: Hannes Reinecke --- drivers/pci/access.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/drivers/pci/access.c b/drivers/pci/access.c index 8449d6b5..01b9d0a 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, -- 2.7.4