On Wed, Aug 02, 2017 at 11:05:58AM -0500, David Lechner wrote:

On 08/02/2017 03:05 AM, Noralf Trønnes wrote:

quoted

Den 02.08.2017 00.26, skrev David Lechner:

quoted

On 08/01/2017 01:08 PM, Noralf Trønnes wrote:

quoted

(cc: Daniel Vetter)


Den 01.08.2017 18.51, skrev David Lechner:

quoted

On 07/30/2017 12:14 PM, Noralf Trønnes wrote:

quoted

Den 29.07.2017 21.40, skrev David Lechner:

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On 07/29/2017 02:17 PM, David Lechner wrote:

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The goal of this series is to get the built-in
LCD of the LEGO MINDSTORMS EV3
working. But, most of the content here is
building up the infrastructure to do
that.

Some general comments/questions:

I have noticed that DRM doesn't really have support
for monochrome displays. I'm guessing that is
because no one really uses them anymore?

The repaper driver was the first monochrome drm driver and I chose to
present it to userspace as XRGB8888 and convert it to monochrome.
The reason for this is that everything, libraries, apps,
plymouth (boot
splash, no rgb565) supports it. I didn't see any point in adding a new
monochrome drm format that didn't have, or probably wouldn't get
userspace support (by libraries at least). The application of course
needs to know this to get a good result.

tinydrm_xrgb8888_to_gray8() does the conversion:
https://cgit.freedesktop.org/drm/drm-misc/commit/drivers/gpu/drm/tinydrm?id=379ea9a1a59a5a32c8db6f164e80a3fd00cb3781

quoted

The LEGO EV3 display is just an LCD (not the backlit
kind). It has two modes of operation. It can to 2bbp
grayscale or it can do 1bpp monochrome. The
grayscale isn't the best (looks splotchy in places),
so it would be nice to be able to choose between
these two modes. How would I implement something
like that?

Do you expect anyone to use grayscale if it doesn't look good?
Maybe better to add it later if there's a demand for it.

I don't expect many people to use it at all. The people that
do will be hackers like me that want to see what it is
capable of, so I think I will keep it grayscale by default.

It looks like the best way to satisfy your needs is to add
specific formats.

Video for Linux have these:

include/uapi/linux/videodev2.h

/* Grey formats */
#define V4L2_PIX_FMT_GREY    v4l2_fourcc('G', 'R', 'E', 'Y') /*
8 Greyscale     */
#define V4L2_PIX_FMT_Y4      v4l2_fourcc('Y', '0', '4', ' ') /*
4 Greyscale     */
#define V4L2_PIX_FMT_Y6      v4l2_fourcc('Y', '0', '6', ' ') /*
6 Greyscale     */
#define V4L2_PIX_FMT_Y10     v4l2_fourcc('Y', '1', '0', ' ') /*
10 Greyscale     */
#define V4L2_PIX_FMT_Y12     v4l2_fourcc('Y', '1', '2', ' ') /*
12 Greyscale     */
#define V4L2_PIX_FMT_Y16     v4l2_fourcc('Y', '1', '6', ' ') /*
16 Greyscale     */
#define V4L2_PIX_FMT_Y16_BE  v4l2_fourcc_be('Y', '1', '6', ' ')
/* 16 Greyscale BE  */


Maybe we can add formats like these:

include/uapi/drm/drm_fourcc.h

#define DRM_FORMAT_MONO        fourcc_code('Y', '0', '1', ' ')
/* [0] Monochrome */
or
#define DRM_FORMAT_Y1        fourcc_code('Y', '0', '1', ' ') /*
[0] Monochrome */

#define DRM_FORMAT_Y2        fourcc_code('Y', '0', '2', ' ') /*
[1:0] Greyscale */

Daniel, what do you think?

2 of the first 3 tinydrm drivers are monochrome (and I would like to
write a driver for the Seeed/Grove I2C OLED displays which are also
monochrome), so I think the 1bpp modes would definitely be useful. I
think there is enough userspace code still around that knows about
FB_VISUAL_MONO01 and FB_VISUAL_MONO10 that could use these.

Can you elaborate, would you use the display trough monochrome fbdev
or through drm?

I have a small collection of programs and libraries that work using
monochrome fbdev. I would like to just keep using them without having to
convert everything to drm.

That probably means we'd need to extend fbdev emulation helpers in drm to
support Monochrome modes better. Shouldn't be that much work really.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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