Revert r233662 and generalize the hack. Writing zero to BAR actually does

not disable it and it is even harmful as hselasky found out.  Historically,
this code was originated from (OLDCARD) CardBus driver and later leaked into
PCI driver when CardBus was newbus'ified and refactored with PCI driver.
However, it is not really necessary even for CardBus.

Reviewed by:	hselasky, imp, jhb

1 files changed, 6 insertions, 41 deletions

diff --git a/sys/dev/pci/pci.c b/sys/dev/pci/pci.c
index 64b3a99..a5b7d4c 100644
--- a/sys/dev/pci/pci.c
+++ b/sys/dev/pci/pci.c
@@ -2590,27 +2590,6 @@ pci_write_bar(device_t dev, struct pci_map *pm, pci_addr_t base)
 	struct pci_devinfo *dinfo;
 	int ln2range;
 
-	/*
-	 * Don't disable BARs on AGP devices. In general: Don't
-	 * disable BARs on any PCI display devices, because doing that
-	 * can sometimes cause the main memory bus to stop working,
-	 * causing all memory reads to return nothing but 0xFFFFFFFF,
-	 * even though the memory location was previously written.
-	 * After a while a privileged instruction fault will appear
-	 * and then nothing more can be debugged.
-	 * The reason for this behaviour is unknown.
-	 */
-	if (base == 0 && pci_get_class(dev) == PCIC_DISPLAY) {
-		device_printf(device_get_parent(dev),
-		    "pci%d:%d:%d:%d BARs on display devices "
-		    "should not be disabled.\n",
-		    pci_get_domain(dev),
-		    pci_get_bus(dev),
-		    pci_get_slot(dev),
-		    pci_get_function(dev));
-		return;
-	}
-
 	/* The device ROM BAR is always a 32-bit memory BAR. */
 	dinfo = device_get_ivars(dev);
 	if (PCIR_IS_BIOS(&dinfo->cfg, pm->pm_reg))
@@ -2838,16 +2817,15 @@ pci_add_map(device_t bus, device_t dev, int reg, struct resource_list *rl,
 	    prefetch ? RF_PREFETCHABLE : 0);
 	if (res == NULL) {
 		/*
-		 * If the allocation fails, clear the BAR and delete
-		 * the resource list entry to force
-		 * pci_alloc_resource() to allocate resources from the
-		 * parent.
+		 * If the allocation fails, delete the resource list entry
+		 * to force pci_alloc_resource() to allocate resources
+		 * from the parent.
 		 */
 		resource_list_delete(rl, type, reg);
-		start = 0;
-	} else
+	} else {
 		start = rman_get_start(res);
-	pci_write_bar(dev, pm, start);
+		pci_write_bar(dev, pm, start);
+	}
 	return (barlen);
 }
 
@@ -4381,19 +4359,6 @@ pci_delete_resource(device_t dev, device_t child, int type, int rid)
 			    type, rid, rman_get_start(rle->res));
 			return;
 		}
-
-#ifndef __PCI_BAR_ZERO_VALID
-		/*
-		 * If this is a BAR, clear the BAR so it stops
-		 * decoding before releasing the resource.
-		 */
-		switch (type) {
-		case SYS_RES_IOPORT:
-		case SYS_RES_MEMORY:
-			pci_write_bar(child, pci_find_bar(child, rid), 0);
-			break;
-		}
-#endif
 		resource_list_unreserve(rl, dev, child, type, rid);
 	}
 	resource_list_delete(rl, type, rid);