MFC 306359

    pci: Clear the MEM/PORT_EN bit when updating PCI BAR

    It's unsafe to update the BAR when the related EN bit is set.

    Submitted by:   Dexuan Cui <decui microsoft com>
    Reviewed by:    jhb
    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D7914

1 files changed, 10 insertions, 0 deletions

diff --git a/sys/dev/pci/pci.c b/sys/dev/pci/pci.c
index bb90375c..9bf37bc 100644
--- a/sys/dev/pci/pci.c
+++ b/sys/dev/pci/pci.c
@@ -4576,6 +4576,7 @@ pci_reserve_map(device_t dev, device_t child, int type, int *rid,
 	struct resource_list *rl = &dinfo->resources;
 	struct resource *res;
 	struct pci_map *pm;
+	uint16_t cmd;
 	pci_addr_t map, testval;
 	int mapsize;
 
@@ -4660,8 +4661,17 @@ pci_reserve_map(device_t dev, device_t child, int type, int *rid,
 		device_printf(child,
 		    "Lazy allocation of %#lx bytes rid %#x type %d at %#lx\n",
 		    count, *rid, type, rman_get_start(res));
+
+	/* Disable decoding via the CMD register before updating the BAR */
+	cmd = pci_read_config(child, PCIR_COMMAND, 2);
+	pci_write_config(child, PCIR_COMMAND,
+	    cmd & ~(PCI_BAR_MEM(map) ? PCIM_CMD_MEMEN : PCIM_CMD_PORTEN), 2);
+
 	map = rman_get_start(res);
 	pci_write_bar(child, pm, map);
+
+	/* Restore the original value of the CMD register */
+	pci_write_config(child, PCIR_COMMAND, cmd, 2);
 out:
 	return (res);
 }