VPD reads can be time-consuming operations, and when reading bytes
sequentially then worst-case we may read the same VPD dword four times.
Typically it happens in pci_vpd_size() already that the same VPD dword
is read more than once. Therefore let's add a simple read cache that
caches the last read VPD dword.
Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx>
---
drivers/pci/vpd.c | 13 +++++++++++++
include/linux/pci.h | 2 ++
2 files changed, 15 insertions(+)
diff --git a/drivers/pci/vpd.c b/drivers/pci/vpd.c
index 75e48df2e..2315e45f6 100644
--- a/drivers/pci/vpd.c
+++ b/drivers/pci/vpd.c
@@ -194,6 +194,11 @@ static ssize_t pci_vpd_read(struct pci_dev *dev, loff_t pos, size_t count,
break;
}
+ if (vpd->cached_offset == (pos & ~3)) {
+ val = vpd->cached_val;
+ goto process;
+ }
+
ret = pci_user_write_config_word(dev, vpd->cap + PCI_VPD_ADDR,
pos & ~3);
if (ret < 0)
@@ -206,6 +211,9 @@ static ssize_t pci_vpd_read(struct pci_dev *dev, loff_t pos, size_t count,
if (ret < 0)
break;
+ vpd->cached_val = val;
+ vpd->cached_offset = pos & ~3;
+process:
skip = pos & 3;
for (i = 0; i < sizeof(u32); i++) {
if (i >= skip) {
@@ -242,6 +250,10 @@ static ssize_t pci_vpd_write(struct pci_dev *dev, loff_t pos, size_t count,
return -EINTR;
while (pos < end) {
+ /* invalidate read cache */
+ if (vpd->cached_offset == pos)
+ vpd->cached_offset = -1;
+
ret = pci_user_write_config_dword(dev, vpd->cap + PCI_VPD_DATA,
get_unaligned_le32(buf));
if (ret < 0)
@@ -270,6 +282,7 @@ void pci_vpd_init(struct pci_dev *dev)
dev->vpd.cap = pci_find_capability(dev, PCI_CAP_ID_VPD);
mutex_init(&dev->vpd.lock);
+ dev->vpd.cached_offset = -1;
}
static ssize_t vpd_read(struct file *filp, struct kobject *kobj,
diff --git a/include/linux/pci.h b/include/linux/pci.h
index cd8aa6fce..fb123c248 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -297,6 +297,8 @@ enum pcie_link_width pcie_get_width_cap(struct pci_dev *dev);
struct pci_vpd {
struct mutex lock;
unsigned int len;
+ u32 cached_val;
+ int cached_offset;
u8 cap;
};
--
2.33.0
