linux-kernel - Re: [PATCH v2] vt: add init_hide parameter to suppress boot output

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Message-ID: <20130221011242.GB4961@kroah.com>
Date:	Wed, 20 Feb 2013 17:12:42 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Andy Ross <andy.ross@...driver.com>
Cc:	Pavel Machek <pavel@....cz>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Jiri Slaby <jslaby@...e.cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Len Brown <len.brown@...el.com>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH v2] vt: add init_hide parameter to suppress boot output

On Wed, Feb 20, 2013 at 02:08:25PM -0800, Andy Ross wrote:
> On 02/20/2013 12:57 PM, Pavel Machek wrote:
> >I'm sure something creative can be done with fake init that shuts
> >the console up then execs previous init. No need to add more kernel
> >knobs, I'd say.
> 
> Fair enough, but some last words:
> 
> That's argument is the "it's about logging" hypothesis again.  Even if
> it were possible to completely shut up console output (something
> that's awfully hard in the general case when running on PC hardware,
> and IMHO from a developer's perspective not even a good thing), that's
> not the whole problem.  The framebuffer console initialization does a
> buffer clear and mode set, and that clobbers anything the bootloader
> might have left on the screen prematurely, before userspace is ready
> to throw up its own splash.  Splash screens may be a silly
> requirement, but they're still a requirement.

Yes, they are a requirement in some situations, and if you look most
distros have already solved this issue for you, by not using a
framebuffer at all.  Why not just do the same thing in your Android
system as you do have full control over the hardware and the boot
process.

> And the suspend console problem is likewise at work: ideally you'd
> like to know, for example, that the panel backlight is off before
> suspending.  But what happens in practice is that the kernel does a VT
> switch to/from console 63 and the backlight wakes up (I'm not going to
> pretend I have this bit completely figured out, but the problem is/was
> real and this patch fixed it by suppressing the console visibility).

My systems don't drop down to the framebuffer when suspending, I think
you need to look at using a better distro :)

> Now, the point that an in-kernel console is "going away" and thus not
> worth augmenting with new APIs is valid.  And this is a small patch
> that's unlikely to be difficult to maintain in a custom tree.  And as
> we all agree there are other mechanisms that can be used here (even if
> AFAICT they don't completely solve the problem), and indeed I'd love
> to get surfaceflinger working with VT_ACTIVATE et. al. if I get a
> chance.  So I'm not going to cry if this isn't worth mainline.

I don't see why this is even needed for surfaceflinger systems, as
again, you have full control over the hardware and system so you don't
even need a framebuffer console at all.

thanks,

greg k-h
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