Message-ID: <CAMj1kXGeGG6hCCNKhSxPJppkTzBeZg9jO0py1P8xfi2N3S=vyQ@mail.gmail.com>
Date: Tue, 26 Aug 2025 10:16:37 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Jan Kiszka <jan.kiszka@...mens.com>
Cc: Aaron Kling <webgeek1234@...il.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 09:23, Jan Kiszka <jan.kiszka@...mens.com> wrote:
>
> On 26.08.25 00:09, Aaron Kling wrote:
> > 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.
> >
>
> That makes sense now, and surely don't mind having some build-time or
> runtime configuration switch that allow to tune the system into such
> settings. It's just not so nice to take away the freedom of full-scale
> loglevel control from the efistub.
>

Yeah, that would be my fault, I guess. I suggested simplifying this to
the current approach.

Would it be sufficient to make the EFI stub loglevel a separate
compile time Kconfig option? I'd prefer that over adding more runtime
logic.

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