[PATCH RESEND] PCI/VPD: Add simple VPD read cache

[Heiner Kallweit <hkallweit1@gmail.com>]

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@gmail.com>
---
 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