linux-kernel - Re: [PATCH] efistub: Lower default log level

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Message-ID: <CALHNRZ_Q9XwJenTVDBdk4NQ79m2wWKRyxNS_sV1TLuqunE_NGQ@mail.gmail.com>
Date: Mon, 25 Aug 2025 17:09:51 -0500
From: Aaron Kling <webgeek1234@...il.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Jan Kiszka <jan.kiszka@...mens.com>, linux-efi@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efistub: Lower default log level

On Mon, Aug 25, 2025 at 4:28 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Tue, 26 Aug 2025 at 02:34, Aaron Kling <webgeek1234@...il.com> wrote:
> >
> > On Mon, Aug 25, 2025 at 5:44 AM Ard Biesheuvel <ardb@...nel.org> wrote:
> > >
> > > On Sun, 24 Aug 2025 at 16:47, Jan Kiszka <jan.kiszka@...mens.com> wrote:
> > > >
> > > > On 24.08.25 02:31, Ard Biesheuvel wrote:
> > > > > On Sat, 16 Aug 2025 at 16:52, Jan Kiszka <jan.kiszka@...mens.com> wrote:
> > > > >>
> > > > >> On 15.07.25 03:35, Ard Biesheuvel wrote:
> > > > >>> On Tue, 8 Jul 2025 at 17:31, Aaron Kling <webgeek1234@...il.com> wrote:
> > > > >>>>
> > > > >>>> On Tue, Jul 8, 2025 at 2:30 AM Aaron Kling via B4 Relay
> > > > >>>> <devnull+webgeek1234.gmail.com@...nel.org> wrote:
> > > > >>>>>
> > > > >>>>> From: Aaron Kling <webgeek1234@...il.com>
> > > > >>>>>
> > > > >>>>> Some uefi implementations will write the efistub logs to the display
> > > > >>>>> over a splash image. This is not desirable for debug and info logs, so
> > > > >>>>> lower the default efi log level to exclude them.
> > > > >>>>>
> > > > >>>>> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> > > > >>>>> Signed-off-by: Aaron Kling <webgeek1234@...il.com>
> > > > >>>>> ---
> > > > >>>>>  drivers/firmware/efi/libstub/printk.c | 4 ++--
> > > > >>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > >>>>>
> > > > >>>>> diff --git a/drivers/firmware/efi/libstub/printk.c b/drivers/firmware/efi/libstub/printk.c
> > > > >>>>> index 3a67a2cea7bdf1aa215d48dbf9ece4ceec6e4c28..bc599212c05dd746a9c54abbbe61a4bf70f1a8c4 100644
> > > > >>>>> --- a/drivers/firmware/efi/libstub/printk.c
> > > > >>>>> +++ b/drivers/firmware/efi/libstub/printk.c
> > > > >>>>> @@ -5,13 +5,13 @@
> > > > >>>>>  #include <linux/ctype.h>
> > > > >>>>>  #include <linux/efi.h>
> > > > >>>>>  #include <linux/kernel.h>
> > > > >>>>> -#include <linux/printk.h> /* For CONSOLE_LOGLEVEL_* */
> > > > >>>>> +#include <linux/kern_levels.h>
> > > > >>>>>  #include <asm/efi.h>
> > > > >>>>>  #include <asm/setup.h>
> > > > >>>>>
> > > > >>>>>  #include "efistub.h"
> > > > >>>>>
> > > > >>>>> -int efi_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
> > > > >>>>> +int efi_loglevel = LOGLEVEL_NOTICE;
> > > > >>>>>
> > > > >>>>>  /**
> > > > >>>>>   * efi_char16_puts() - Write a UCS-2 encoded string to the console
> > > > >>>>>
> > > > >>>>> ---
> > > > >>>>> base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
> > > > >>>>> change-id: 20250708-efi-default-loglevel-4da5a36cac87
> > > > >>>>>
> > > > >>>>> Best regards,
> > > > >>>>> --
> > > > >>>>> Aaron Kling <webgeek1234@...il.com>
> > > > >>>>
> > > > >>>> This patch was originally suggested a few months ago [0], but as far
> > > > >>>> as I can tell was never queued for merge. Since I'm also hitting a
> > > > >>>> case where this is relevant, I'm sending this in to bring attention
> > > > >>>> back to it.
> > > > >>>>
> > > > >>>
> > > > >>> I've queued this up now - thanks.
> > > > >>>
> > > > >>
> > > > >> And how can I get back the loglevel info? It seems I can only choose
> > > > >> between notice, silent and debug now. And the latter two only by also
> > > > >> touching the kernel's loglevel.
> > > > >>
> > > > >> I'm particularly missing [1] in my UART logs now which is helpful in
> > > > >> understanding this essential system state.
> > > > >>
> > > > >
> > > > > Hi Jan,
> > > > >
> > > > > Is efi=debug too noisy for you?
> > > >
> > > > Yes, also because it affects the kernel even more. I'm looking for
> > > > "efi=info".
> > > >
> > > > I don't get the reason behind this change anymore as well. If you have a
> > > > splash screen shown, weren't you booting with "quiet" before already,
> > > > thus also without any stub messages?
> > > >
> > >
> > > Yeah, good point. IIRC that came up in the discussion but I can't
> > > remember the motivation so it can't have been very convincing.
> > >
> > > So should we just revert this change?
> >
> > I'd prefer not to have to set quiet to get a clean splash screen. That
> > doesn't seem like an unreasonable expectation, getting default
> > non-debug logs and not having stuff written on top of the splash
> > image.
>
> Perhaps you could remind us why this only applies to the efistub
> output, and having the output of the kernel itself corrupting the
> splash screen is fine?

I'm not greatly knowledgeable about the efi standard and what's
happening under the hood, so I will just speak to what I saw in my use
case. I'm working on Nvidia Tegra devices, newer generations of which
use EDK2 as the last stage bootloader. The target os is Android, which
has a pretty strictly controlled defconfig. Prior to this change, the
kernel efistub logs were getting passed to the efi impl, which was
then printing those lines to the display. The kernel logs were not
being printed to the screen, as none of the console drivers were
enabled to do so. So after this change, regardless of the kernel log
level, the boot splash will remain untouched until the kernel display
driver takes over the display and the os renders to it. Because no
efistub log lines are being printed.

Aaron