Re: [PATCH v3 0/3] Add generic framebuffer support to EFI earlycon driver

[Markuss Broks <markuss.broks@gmail.com>]

Hi Ard,

On 12/23/22 16:42, Ard Biesheuvel wrote:
> (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.

I believe I must be hitting some other bug then, since my driver should 
not use `struct screen_info` when the arguments are specified manually 
(e.g. in device-tree or in kernel command line options), and it still is 
broken on ARM when they are. I got it to work on ARM when I moved the 
early console initialization later into the kernel booting process, but 
that mostly defeats the purpose of early console driver, I believe. I've 
been thinking that it could be some stuff not getting initialized early 
enough indeed, but I've got no clue what could it be.

>
> 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
>>
- Markuss


P.S. Just noticed I forgot to Ctrl^S the cover letter before saving... 
The main change v3 does is separate the moving action and edit action 
into two separate commits, I don't think there're more major changes. 
With v4 I'd try to attach the proper version log.