[PATCH] x86/PCI: revert "Ignore E820 reservations for bridge windows on newer systems"

[Hans de Goede]

Commit 7f7b4236f204 ("x86/PCI: Ignore E820 reservations for bridge windows
on newer systems") fixes the touchpad not working on laptops like
the Lenovo IdeaPad 3 15IIL05 and the Lenovo IdeaPad 5 14IIL05, as well as
fixing thunderbolt hotplug issues on the Lenovo Yoga C940.

Unfortunately it turns out that this is causing issues with suspend/resume
on Lenovo ThinkPad X1 Carbon Gen 2 laptops. So, per the no regressions
policy, rever this. Note I'm looking into another fix for the issues this
fixed.

Fixes: 7f7b4236f204 ("x86/PCI: Ignore E820 reservations for bridge windows on newer systems")
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=2029207
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
 arch/x86/kernel/resource.c | 23 +----------------------
 1 file changed, 1 insertion(+), 22 deletions(-)

diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
index 9ae64f9af956..9b9fb7882c20 100644
--- a/arch/x86/kernel/resource.c
+++ b/arch/x86/kernel/resource.c
@@ -1,5 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-#include <linux/dmi.h>
 #include <linux/ioport.h>
 #include <asm/e820/api.h>
 
@@ -24,31 +23,11 @@ static void resource_clip(struct resource *res, resource_size_t start,
 		res->start = end + 1;
 }
 
-/*
- * Some BIOS-es contain a bug where they add addresses which map to
- * system RAM in the PCI host bridge window returned by the ACPI _CRS
- * method, see commit 4dc2287c1805 ("x86: avoid E820 regions when
- * allocating address space"). To avoid this Linux by default excludes
- * E820 reservations when allocating addresses since 2010.
- * In 2019 some systems have shown-up with E820 reservations which cover
- * the entire _CRS returned PCI host bridge window, causing all attempts
- * to assign memory to PCI BARs to fail if Linux uses E820 reservations.
- *
- * Ideally Linux would fully stop using E820 reservations, but then
- * the old systems this was added for will regress.
- * Instead keep the old behavior for old systems, while ignoring the
- * E820 reservations for any systems from now on.
- */
 static void remove_e820_regions(struct resource *avail)
 {
-	int i, year = dmi_get_bios_year();
+	int i;
 	struct e820_entry *entry;
 
-	if (year >= 2018)
-		return;
-
-	pr_info_once("PCI: Removing E820 reservations from host bridge windows\n");
-
 	for (i = 0; i < e820_table->nr_entries; i++) {
 		entry = &e820_table->entries[i];
 
-- 
2.33.1