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

From: Will Deacon <will.deacon@arm.com>
To: Chen Gang <gang.chen@asianux.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Catalin Marinas <Catalin.Marinas@arm.com>,
	Arnd Bergmann <arnd@arndb.de>, Tony Lindgren <tony@atomide.com>,
	Santosh Shilimkar <santosh.shilimkar@ti.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] arm64: kernel: need extern variable 'screen_info' for related driver using.
Date: Tue, 21 May 2013 10:03:36 +0100	[thread overview]
Message-ID: <20130521090336.GC10453@mudshark.cambridge.arm.com> (raw)
In-Reply-To: <519B278B.6030708@asianux.com>

On Tue, May 21, 2013 at 08:51:39AM +0100, Chen Gang wrote:
> On 05/21/2013 02:57 PM, Geert Uytterhoeven wrote:
> > On Tue, May 21, 2013 at 5:15 AM, Chen Gang <gang.chen@asianux.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'" ?

We can add the screen_info if and when we need to support a VGA console. In
the meantime, let's not add things on a whim.

> >> > 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.

That's a weak argument. You might as well propose the cleanup and see what
people say.

> 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'.

Erm. PERF_EVENTS, BPF_JIT, IDE, ...?

> 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.

Sure, it works, but we're just contributing to the mess that's been built up
ever time another architecture has done the same thing. It's not hard to try
and clean it up.

Will