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

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Date:   Wed, 9 Feb 2022 19:46:06 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Myron Stowe <myron.stowe@...hat.com>,
        Juha-Pekka Heikkila <juhapekka.heikkila@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Benoit Grégoire <benoitg@...us.ca>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hui Wang <hui.wang@...onical.com>
Subject: Re: [PATCH] x86/PCI: revert "Ignore E820 reservations for bridge
 windows on newer systems"

On Wed, Feb 9, 2022 at 5:14 PM Hans de Goede <hdegoede@...hat.com> wrote:
>
> 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@...hat.com>

Applied as 5.17-rc material and pushed out for -next, thanks!

> ---
>  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
>