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

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Message-ID: <20150313202521.0a4607c3@maestro.intranet>
Date:	Fri, 13 Mar 2015 20:25:21 +0100
From:	Thomas Niederprüm <niederp@...sik.uni-kl.de>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
Cc:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	<linux-fbdev@...r.kernel.org>, <plagnioj@...osoft.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] fbdev: ssd1307fb: Add module parameter
 bitsperpixel.

Am Tue, 10 Mar 2015 12:45:49 +0200
schrieb Tomi Valkeinen <tomi.valkeinen@...com>:

> On 14/02/15 17:54, Maxime Ripard wrote:
> > 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.
> 
> Right, I'm not thrilled =). I don't think it's a good idea to lie to
> the userspace (except when fixing regressions).

Ok, since Maxime and you agree that this is not desirable I will drop
that patch in v4.

Thomas
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