Currently QEMU defaults to a resolution of 1024x768 when exposing EDID
info to the guest OS. The EDID default info is important as this will
influence what resolution many guest OS will configure the screen with
on boot. It can also potentially influence what resolution the firmware
will configure the screen with, though until very recently EDK2 would
not handle EDID info.

One important thing to bear in mind is that the default graphics card
driver provided by Windows will leave the display set to whatever
resolution was enabled by the firmware on boot. Even if sufficient
VRAM is available, the resolution can't be changed without installing
new drivers. IOW, the default resolution choice is quite important
for usability of Windows.

Modern real world monitor hardware for desktop/laptop has supported
resolutions higher than 1024x768 for a long time now, perhaps as long
as 15+ years. There are quite a wide variety of native resolutions in
use today, however, and in wide screen form factors the height may not
be all that tall.

None the less, it is considered that there is scope for making the
QEMU default resolution slightly larger.

In considering what possible new default could be suitable, choices
considered were 1280x720 (720p), 1280x800 (WXGA) and 1280x1024 (SXGA).

In many ways, vertical space is the most important, and so 720p was
discarded due to loosing vertical space, despite being 25% wider.

The SXGA resolution would be good, but when taking into account
window titlebars/toolbars and window manager desktop UI, this might
be a little too tall for some users to fit the guest on their physical
montior.

This patch thus suggests a modest change to 1280x800 (WXGA). This
only consumes 1 MB per colour channel, allowing double buffered
framebuffer in 8 MB of VRAM. Width wise this is 25% larger than
QEMU's current default, but height wise this only adds 5%, so the
difference isn't massive on the QEMU side.

Overall there doesn't appear to be a compelling reason to stick
with 1024x768 resolution.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20211129140508.1745130-1-berrange@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

So we only write out that part of the edid blob
which has been filled with data.
Also use a larger buffer for the blob.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20210427150824.638359-1-kraxel@redhat.com
Message-Id: <20210427150824.638359-2-kraxel@redhat.com>

Not needed and makes some compilers error out with:

qemu-edid.c:15:1: error: initializer element is not constant

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20201013091615.14166-1-kraxel@redhat.com

Replace dpi with width_mm/height_mm in qemu_edid_info.

Use it when set (non-zero) to compute the DPI and generate the EDID.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20200927145751.365446-3-marcandre.lureau@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

No header includes qemu-common.h after this commit, as prescribed by
qemu-common.h's file comment.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190523143508.25387-5-armbru@redhat.com>
[Rebased with conflicts resolved automatically, except for
include/hw/arm/xlnx-zynqmp.h hw/arm/nrf51_soc.c hw/arm/msf2-soc.c
block/qcow2-refcount.c block/qcow2-cluster.c block/qcow2-cache.c
target/arm/cpu.h target/lm32/cpu.h target/m68k/cpu.h target/mips/cpu.h
target/moxie/cpu.h target/nios2/cpu.h target/openrisc/cpu.h
target/riscv/cpu.h target/tilegx/cpu.h target/tricore/cpu.h
target/unicore32/cpu.h target/xtensa/cpu.h; bsd-user/main.c and
net/tap-bsd.c fixed up]

EDID is a metadata format to describe monitors.  On physical hardware
the monitor has an eeprom with that data block which can be read over
i2c bus.

On a linux system you can usually find the EDID data block in
/sys/class/drm/$card/$connector/edid.  xorg ships a edid-decode utility
which you can use to turn the blob into readable form.

I think it would be a good idea to use EDID for virtual displays too.
Needs changes in both qemu and guest kms drivers.  This patch is the
first step, it adds an generator for EDID blobs to qemu.  Comes with a
qemu-edid test tool included.

With EDID we can pass more information to the guest.  Names and serial
numbers, so the guests display configuration has no boring "Unknown
Monitor".  List of video modes.  Display resolution, pretty important
in case we want add HiDPI support some day.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20180925075646.25114-2-kraxel@redhat.com