linux-kernel - Re: [PATCH] arm64: kernel: need extern variable 'screen

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Date:	Tue, 21 May 2013 13:07:58 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	Will Deacon <will.deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Tony Lindgren <tony@...mide.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: kernel: need extern variable 'screen_info' for
 related driver using.

On Tue, May 21, 2013 at 9:51 AM, Chen Gang <gang.chen@...anux.com> wrote:
> On 05/21/2013 02:57 PM, Geert Uytterhoeven wrote:
>> On Tue, May 21, 2013 at 5:15 AM, Chen Gang <gang.chen@...anux.com> 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"
        depends on ARCH_MAY_HAVE_PC_FDC

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...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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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