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

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Date:	Tue, 21 May 2013 19:40:52 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
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 05/21/2013 07:07 PM, Geert Uytterhoeven wrote:
> 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.
> 

Oh, really it is, we need consider them both.


>>>>> >>> > 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.
> 

Hmm..., it seems so, but I think we'd better to discuss it with the
'final applier' firstly.


>> > 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.
> 

Oh, really, it is !!

Hmm.., most of current machines do not have floppy, now, and will be
less and less in the future, it has to use the variables in this way to
avoid a very very very long list (not only include architectures, but
also include the each features companition) !!

But for VIDEO_CONSOL, most of machines need it, and will be more and
more in the future (maybe arm64 will also support it, too, in the future).

So...


>> > 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...

I suggest better to discuss it with the 'final applier' firstly.

Good Luck !!


Thanks.
-- 
Chen Gang

Asianux Corporation
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