misc: pch_phub: Read prefetch value from device tree if passed

The default prefetch value for the eg20t device is hard coded to
0x000affaa.

Add support for an alternative to be read from DT if available
Signed-off-by: NZubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/pch_phub.c

@@ -28,6 +28,7 @@
 #include <linux/if_ether.h>
 #include <linux/ctype.h>
 #include <linux/dmi.h>
+#include <linux/of.h>
 
 #define PHUB_STATUS 0x00		/* Status Register offset */
 #define PHUB_CONTROL 0x04		/* Control Register offset */
@@ -711,6 +712,12 @@ static int pch_phub_probe(struct pci_dev *pdev,
 
 	if (id->driver_data == 1) { /* EG20T PCH */
 		const char *board_name;
+		unsigned int prefetch = 0x000affaa;
+
+		if (pdev->dev.of_node)
+			of_property_read_u32(pdev->dev.of_node,
+						  "intel,eg20t-prefetch",
+						  &prefetch);
 
 		ret = sysfs_create_file(&pdev->dev.kobj,
 					&dev_attr_pch_mac.attr);
@@ -736,7 +743,7 @@ static int pch_phub_probe(struct pci_dev *pdev,
 						CLKCFG_UART_MASK);
 
 		/* set the prefech value */
-		iowrite32(0x000affaa, chip->pch_phub_base_address + 0x14);
+		iowrite32(prefetch, chip->pch_phub_base_address + 0x14);
 		/* set the interrupt delay value */
 		iowrite32(0x25, chip->pch_phub_base_address + 0x44);
 		chip->pch_opt_rom_start_address = PCH_PHUB_ROM_START_ADDR_EG20T;