linux-kernel - Re: [PATCH 5/8] fbdev: ssd1307fb: Add module parameter bitsperpixel.

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Message-ID: <20150214155415.GC25269@lukather>
Date:	Sat, 14 Feb 2015 16:54:15 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Thomas Niederprüm <niederp@...sik.uni-kl.de>
Cc:	linux-fbdev@...r.kernel.org, plagnioj@...osoft.com,
	tomi.valkeinen@...com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] fbdev: ssd1307fb: Add module parameter bitsperpixel.

On Sat, Feb 07, 2015 at 05:05:03PM +0100, Thomas Niederprüm wrote:
> Am Sat, 7 Feb 2015 12:20:43 +0100
> schrieb Maxime Ripard <maxime.ripard@...e-electrons.com>:
> 
> > On Fri, Feb 06, 2015 at 11:28:11PM +0100, niederp@...sik.uni-kl.de
> > wrote:
> > > From: Thomas Niederprüm <niederp@...sik.uni-kl.de>
> > > 
> > > This patch adds a module parameter 'bitsperpixel' to adjust the
> > > colordepth of the framebuffer. All values >1 will result in memory
> > > map of the requested color depth. However only the MSB of each
> > > pixel will be sent to the device. The framebuffer identifies itself
> > > as a grayscale display with the specified depth.
> > 
> > I'm not sure this is the right thing to do.
> > 
> > The bits per pixel for this display is rightfully defined, used and
> > reported to the userspace, why would you want to change that?
> 
> You are right of course. The display is 1bpp and it reports to be 1
> bpp. The problem is that there is almost no userspace library that can
> handle 1 bit framebuffers correctly. So it is nice if the framebuffer
> (optionally) can expose itself as 8 bits per pixel grayscale to the
> userspace program. As an example this allows to run DirectFB on the
> framebuffer, which is not possible out of the box for 1bpp.
> 
> Also note that if do not set the module parameter at load time
> the framebuffer will be 1bpp. So you have to actively set that module
> parameter to make the framebuffer pretend to be more than 1bpp.
> 
> In any case I don't cling to that patch, I just thought it was a nice
> feature.

I'd say that the right fix would be to patch DirectFB, instead of
faking that in the kernel.

But again, that's probably Tomi's call, not mine.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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