Re: [PATCH] arm64: kernel: need extern variable 'screen_info' forrelated driver using.

From: Geert Uytterhoeven
Date: Tue May 21 2013 - 07:08:04 EST

On Tue, May 21, 2013 at 9:51 AM, Chen Gang <gang.chen@xxxxxxxxxxx> wrote:
> On 05/21/2013 02:57 PM, Geert Uytterhoeven wrote:
>> On Tue, May 21, 2013 at 5:15 AM, Chen Gang <gang.chen@xxxxxxxxxxx> wrote:
>>>> >> I think it would be better if we added a something like
>>>> >> CONFIG_HAVE_VGA_CONSOLE, which VGA_CONSOLE can then depend on. Architectures
>>>> >> like x86 can then select the former, and we can remove the long list of
>>>> >> architectures from the current option.
>>> >
>>> > I guess your meaning is:
>>> >
>>> > under arm64, actually, need not support 'VGA_CONSOLE', and 'screen_info' is useless.
>>> > So better to define 'CONFIG_HAVE_VGA_CONSOLE' which 'VGA_CONSOLE' can depend on it, and in arm64, we do not define CONFIG_HAVE_VGA_CONSOLE.
>>> >
>>> > Is it correct ?
>> No, you missed "and we can remove the long list of architectures from the
>> current option".
> OK, thanks.
> Is it correct: "it is unnecessary to add 'screen_info' to the code, for
> arm64 will never support 'VGA_CONSOLE'" ?

On arm (not (yet?) arm64), drivers/video/console/dummycon.c also uses
screen_info. The default text mode resolution may come from atags.

>>> > If so, I recommend to add depend item for VGA_CONSOLE directly:
>> I strongly support CONFIG_HAVE_VGA_CONSOLE.
> For me, I still recommend add 'ARM64' in the long list of architectures
> for 'VGA_CONSOLE', I have 3 reasons, please check:
> a. current implementation only changes one area which only related with
> arm64 and 'VGA_CONSOLE', but if use 'CONFIG_HAVE_VGA_CONSOLE', that will
> touch many multiple platforms dependency, at least we need discuss about
> it with multiple platforms guys for it, firstly.

Sure. But this can be one cleanup patch.

> b. We can find some cases to use CONFIG_HAVE_* as dpend on, but I can
> not find any cases which let CONFIG_'samename' depend on
> CONFIG_HAVE_'samename'.

A similar mechanism is used for PC-style floppy support, but the naming
is different, cfr. drivers/block/Kconfig:

config BLK_DEV_FD
tristate "Normal floppy disk support"

so perhaps ARCH_MAY_HAVE_VGA?

PARPORT_PC could use the same mechanism.

> c. The original way still has effect, although it seems not quit
> beautiful, but it is correct and still clear for readers, it is still
> sustainable.

Most/every new architecture needs to add a depend to it.

BTW, I should have done this when sending out the patch to add CRIS to the
list of dependencies...



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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