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References: <20221221105402.6598-1-markuss.broks@gmail.com>
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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Fri, 23 Dec 2022 15:42:33 +0100
Message-ID: <CAMj1kXGUC7dsSwVEUsAMeAoqDYtbqrM7SDOJTXbPfi-LrcSk9g@mail.gmail.com>
Subject: Re: [PATCH v3 0/3] Add generic framebuffer support to EFI earlycon driver
To:     Markuss Broks <markuss.broks@gmail.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     linux-kernel@vger.kernel.org,
        Jami Kettunen <jami.kettunen@protonmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Helge Deller <deller@gmx.de>, Borislav Petkov <bp@suse.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Will Deacon <will@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Muchun Song <muchun.song@linux.dev>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        Kim Phillips <kim.phillips@amd.com>, linux-doc@vger.kernel.org,
        linux-efi@vger.kernel.org, linux-serial@vger.kernel.org,
        linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org
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(cc Andy)


On Wed, 21 Dec 2022 at 11:54, Markuss Broks <markuss.broks@gmail.com> wrote:
>
> Make the EFI earlycon driver be suitable for any linear framebuffers.
> This should be helpful for early porting of boards with no other means of
> output, like smartphones/tablets. There seems to be an issue with early_ioremap
> function on ARM32, but I am unable to find the exact cause. It appears the mappings
> returned by it are somehow incorrect, thus the driver is disabled on ARM.

The reason that this driver is disabled on ARM is because the struct
screen_info is not populated early enough, as it is retrieved from a
UEFI configuration table.

early_ioremap() works fine on ARM as long as they mapping is torn down
before paging_init()

> EFI early
> console was disabled on IA64 previously because of missing early_memremap_prot,
> and this is inherited to this driver.
>
> This patch also changes

"This patch also changes ..." is usually a strong hint to self that
the patches need to be split up.

> behavior on EFI systems, by selecting the mapping type
> based on if the framebuffer region intersects with system RAM. If it does, it's
> common sense that it should be in RAM as a whole, and so the system RAM mapping is
> used. It was tested to be working on my PC (Intel Z490 platform), as well as several
> ARM64 boards (Samsung Galaxy S9 (Exynos), iPad Air 2, Xiaomi Mi Pad 4, ...).
>
> Markuss Broks (2):
>   drivers: serial: earlycon: Pass device-tree node
>   efi: earlycon: Add support for generic framebuffers and move to fbdev
>     subsystem
>
>
> v1 -> v2:
>
> - a new patch correcting serial/earlycon.c argument name to "offset" instead
>   of "node"
> - move IA64 exclusion from EFI earlycon Kconfig to earlycon driver Kconfig
>   (IA64 has no early_memremap_prot)
> - move driver from fbdev to console subsystem
> - select EFI earlycon by default
> - fetch stride manually from device-tree, as on some devices it seems stride
>   doesn't match the horizontal resolution * bpp.
> - use saner format (e.g. 1920x1080x32 instead of 1920,1080,32).
>
>
> Markuss Broks (3):
>   drivers: serial: earlycon: Pass device-tree node
>   efi: earlycon: move to video/console to prepare for changes
>   efi: earlycon: Add support for generic framebuffers
>
>  .../admin-guide/kernel-parameters.txt         |  12 +-
>  MAINTAINERS                                   |   5 +
>  drivers/firmware/efi/Kconfig                  |   7 +-
>  drivers/firmware/efi/Makefile                 |   1 -
>  drivers/firmware/efi/earlycon.c               | 246 --------------
>  drivers/tty/serial/earlycon.c                 |   3 +
>  drivers/video/console/Kconfig                 |  11 +
>  drivers/video/console/Makefile                |   1 +
>  drivers/video/console/earlycon.c              | 305 ++++++++++++++++++
>  include/linux/serial_core.h                   |   1 +
>  10 files changed, 336 insertions(+), 256 deletions(-)
>  delete mode 100644 drivers/firmware/efi/earlycon.c
>  create mode 100644 drivers/video/console/earlycon.c
>
> --
> 2.39.0
>