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

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Message-ID: <CAMj1kXE9tNa5R22M9NTmLY8qtnpxbvqMG-Cw0vFpVtr_KoM9bA@mail.gmail.com>
Date: Tue, 26 Aug 2025 07:28:33 +1000
From: Ard Biesheuvel <ardb@...nel.org>
To: Aaron Kling <webgeek1234@...il.com>
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 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?

> But if this needs to be reverted, It would be nice to have an
> option like the original patch which allowed setting the efi loglevel
> separately. Or perhaps leave this as is and add the option to turn up
> the efi loglevel independently.
>

Let's go back to the beginning and figure out to which problem this is
the solution.