[3/4] dummycon: limit Arm console size hack to footbridge

  From: Arnd Bergmann <arnd@arndb.de>

The dummycon default console size used to be determined by architecture,
but now this is a Kconfig setting on everything except ARM. Tracing this
back in the historic git trees, this was used to match the size of VGA
console or VGA framebuffer on early machines, but nowadays that code is
no longer used, except probably on the old footbridge/netwinder since
that is the only one that supports vgacon.

On machines with a framebuffer, booting with DT so far results in always
using the hardcoded 80x30 size in dummycon, while on ATAGS the setting
can come from a bootloader specific override. Both seem to be worse
choices than the Kconfig setting, since the actual text size for fbcon
also depends on the selected font.

Make this work the same way as everywhere else and use the normal
Kconfig setting, except for the footbridge with vgacon, which keeps
using the traditional code. If vgacon is disabled, footbridge can
also ignore the setting. This means the screen_info only has to be
provided when either vgacon or EFI are enabled now.

To limit the amount of surprises on Arm, change the Kconfig default
to the previously used 80x30 setting instead of the usual 80x25.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/arm/kernel/atags_parse.c    | 2 +-
 arch/arm/kernel/setup.c          | 3 +--
 drivers/video/console/Kconfig    | 5 +++--
 drivers/video/console/dummycon.c | 2 +-
 4 files changed, 6 insertions(+), 6 deletions(-)
  

On Fri, Jul 7, 2023 at 11:56 AM Arnd Bergmann <arnd@kernel.org> wrote:

> From: Arnd Bergmann <arnd@arndb.de>
>
> The dummycon default console size used to be determined by architecture,
> but now this is a Kconfig setting on everything except ARM. Tracing this
> back in the historic git trees, this was used to match the size of VGA
> console or VGA framebuffer on early machines, but nowadays that code is
> no longer used, except probably on the old footbridge/netwinder since
> that is the only one that supports vgacon.
>
> On machines with a framebuffer, booting with DT so far results in always
> using the hardcoded 80x30 size in dummycon, while on ATAGS the setting
> can come from a bootloader specific override. Both seem to be worse
> choices than the Kconfig setting, since the actual text size for fbcon
> also depends on the selected font.
>
> Make this work the same way as everywhere else and use the normal
> Kconfig setting, except for the footbridge with vgacon, which keeps
> using the traditional code. If vgacon is disabled, footbridge can
> also ignore the setting. This means the screen_info only has to be
> provided when either vgacon or EFI are enabled now.
>
> To limit the amount of surprises on Arm, change the Kconfig default
> to the previously used 80x30 setting instead of the usual 80x25.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Tested this before and after patch and it looks the same on the NetWinder.
Tested-by: Linus Walleij <linus.walleij@linaro.org>

The legacy in the cyber2000 FB driver supports pseudocolor which
makes it a bit hard to rewrite into a simple DRM driver, which is something
I could otherwise look into, it's not a very big or complex driver
after all.

Yours,
Linus Walleij
  

Arnd Bergmann <arnd@kernel.org> writes:

> From: Arnd Bergmann <arnd@arndb.de>
>
> The dummycon default console size used to be determined by architecture,
> but now this is a Kconfig setting on everything except ARM. Tracing this
> back in the historic git trees, this was used to match the size of VGA
> console or VGA framebuffer on early machines, but nowadays that code is
> no longer used, except probably on the old footbridge/netwinder since
> that is the only one that supports vgacon.
>
> On machines with a framebuffer, booting with DT so far results in always
> using the hardcoded 80x30 size in dummycon, while on ATAGS the setting
> can come from a bootloader specific override. Both seem to be worse
> choices than the Kconfig setting, since the actual text size for fbcon
> also depends on the selected font.
>
> Make this work the same way as everywhere else and use the normal
> Kconfig setting, except for the footbridge with vgacon, which keeps
> using the traditional code. If vgacon is disabled, footbridge can
> also ignore the setting. This means the screen_info only has to be
> provided when either vgacon or EFI are enabled now.
>
> To limit the amount of surprises on Arm, change the Kconfig default
> to the previously used 80x30 setting instead of the usual 80x25.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
  

On Fri, Jul 7, 2023, at 13:33, Linus Walleij wrote:
> On Fri, Jul 7, 2023 at 11:56 AM Arnd Bergmann <arnd@kernel.org> wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>>
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> Tested this before and after patch and it looks the same on the NetWinder.
> Tested-by: Linus Walleij <linus.walleij@linaro.org>

Great, thanks for testing!

> The legacy in the cyber2000 FB driver supports pseudocolor which
> makes it a bit hard to rewrite into a simple DRM driver, which is something
> I could otherwise look into, it's not a very big or complex driver
> after all.

Not sure if that's worth it, my feeling is that we are stuck with
fbdev on a lot of other workstations of the era, so unless someone
puts significant energy into converting all the others as well, there
is little benefit of changing this one. It would be a little different
on platforms that actually run a regular Debian distro kernel that
is shared with modern machines.

Since you have already spent the time to build and test a kernel with
this patch, can you do one more test here and check the text size
reported in the atags on this machine and the actual text sizes you
get from both vgacon and cyber2000fb?

     Arnd
  

On Fri, Jul 7, 2023 at 4:28 PM Arnd Bergmann <arnd@arndb.de> wrote:

> Since you have already spent the time to build and test a kernel with
> this patch, can you do one more test here and check the text size
> reported in the atags on this machine and the actual text sizes you
> get from both vgacon and cyber2000fb?

Heh I tested this then walked out of the office for vacation.

But I can put a note in my calendar to test it when I return to
my equipment!

Yours,
Linus Walleij