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

Am Tue, 10 Mar 2015 12:45:49 +0200
schrieb Tomi Valkeinen [off-list ref]:

On 14/02/15 17:54, Maxime Ripard wrote:

quoted

On Sat, Feb 07, 2015 at 05:05:03PM +0100, Thomas Niederprüm wrote:

quoted

Am Sat, 7 Feb 2015 12:20:43 +0100
schrieb Maxime Ripard [off-list ref]:

quoted

On Fri, Feb 06, 2015 at 11:28:11PM +0100, niederp@physik.uni-kl.de
wrote:

quoted

From: Thomas Niederprüm <redacted>

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