DRM/KMS framebuffer emulation - How to set format

[jhi]

Using the KMS/DRM driver, how can I change the emulated framebuffer format? I'm using simple-panel and the framebuffer has always only 16-bit color even though the driver explicit sets the format for 24-bit colors (.bus_format = MEDIA_BUS_FMT_RGB888_1X24).

fbset doesn't work:

fbset -g 800 480 800 480 24
fbset: FBIOPUT_VSCREENINFO: Invalid argument

modetest

modetest -M stm
Encoders:
id crtc type possible crtcs possible clones
32 38 DPI 0x00000001 0x00000001
 
Connectors:
id encoder status name size (mm) modes encoders
33 32 connected DPI-1 154x86 1 32
 modes:
 index name refresh (Hz) hdisp hss hse htot vdisp vss vse vtot
 #0 800x480 57.29 800 1010 1011 1057 480 503 523 545 33000 flags: ; type: preferred, driver
 props:
 1 EDID:
 flags: immutable blob
 blobs:
 
 value:
 2 DPMS:
 flags: enum
 enums: On=0 Standby=1 Suspend=2 Off=3
 value: 0
 5 link-status:
 flags: enum
 enums: Good=0 Bad=1
 value: 0
 6 non-desktop:
 flags: immutable range
 values: 0 1
 value: 0
 4 TILE:
 flags: immutable blob
 blobs:
 
 value:
 
CRTCs:
id fb pos size
38 43 (0,0) (800x480)
 #0 800x480 57.29 800 1010 1011 1057 480 503 523 545 33000 flags: ; type: preferred, driver
 props:
 24 VRR_ENABLED:
 flags: range
 values: 0 1
 value: 0
 31 BACKGROUND_COLOR:
 flags: range
 values: 0 18446744073709551615
 value: 18446462598732840960
 28 GAMMA_LUT:
 flags: blob
 blobs:
 
 value:
 29 GAMMA_LUT_SIZE:
 flags: immutable range
 values: 0 4294967295
 value: 256
 
Planes:
id crtc fb CRTC x,y x,y gamma size possible crtcs
34 38 43 0,0 0,0 0 0x00000001
 formats: AR24 XR24 RG24 RG16 AR15 XR15 AR12 XR12 C8
 props:
 8 type:
 flags: immutable enum
 enums: Overlay=0 Primary=1 Cursor=2
 value: 1
 30 IN_FORMATS:
 flags: immutable blob
 blobs:
 
 value:
 01000000000000000900000018000000
 01000000400000004152323458523234
 52473234524731364152313558523135
 41523132585231324338202000000000
 ff010000000000000000000000000000
 0000000000000000
 in_formats blob decoded:
 AR24: LINEAR
 XR24: LINEAR
 RG24: LINEAR
 RG16: LINEAR
 AR15: LINEAR
 XR15: LINEAR
 AR12: LINEAR
 XR12: LINEAR
 C8 : LINEAR
 36 alpha:
 flags: range
 values: 0 65535
 value: 65535
 37 zpos:
 flags: immutable range
 values: 0 0
 value: 0
39 0 0 0,0 0,0 0 0x00000001
 formats: AR24 RG24 RG16 AR15 AR12 C8
 props:
 8 type:
 flags: immutable enum
 enums: Overlay=0 Primary=1 Cursor=2
 value: 0
 30 IN_FORMATS:
 flags: immutable blob
 blobs:
 
 value:
 01000000000000000600000018000000
 01000000300000004152323452473234
 52473136415231354152313243382020
 3f000000000000000000000000000000
 0000000000000000
 in_formats blob decoded:
 AR24: LINEAR
 RG24: LINEAR
 RG16: LINEAR
 AR15: LINEAR
 AR12: LINEAR
 C8 : LINEAR
 41 alpha:
 flags: range
 values: 0 65535
 value: 65535
 42 zpos:
 flags: immutable range
 values: 1 1
 value: 1
 
Frame buffers:
id size pitch

modetest -M stm -s 33@32:800x480-57.29@XR24 &
# failed to find CRTC for pipe
failed to create dumb buffer: Invalid argument

[jhi]

fbset

mode "800x480-0"
 # D: 0.000 MHz, H: 0.000 kHz, V: 0.000 Hz
 geometry 800 480 800 480 16
 timings 0 0 0 0 0 0 0
 accel true
 rgba 5/11,6/5,5/0,0/0
endmode

I also tried to change the kernel driver (drivers/gpu/drm/stm/drv.c), by adding

ddev->mode_config.preferred_depth = 24;

but it didn't change anything.

[OlivierK]

Hi jhi (Community Member)

According to your settings CRTC ID seems to be equal to 38 (not 32).

What about if you try modetest -M stm -s 33@38:800x480-57.29@XR24 &

Regards,

Olivier

[jhi]

Well the command "works" and it shows the test image, but I can't say if it is 24-bit or not because it seems that the mode lasts only as long the modetest is running. If it really sets it persistent, I can't see any difference with my test image and fbset shows the same as before.

# modetest -M stm -s 33@38:800x480-57.29@XR24 -d &
# setting mode 800x480-57.29Hz on connectors 33, crtc 38
 
[1]+ Done modetest -M stm -s 33@38:800x480-57.29@XR24 -d

How can I set this mode to be persistent or default? Are there any other ways to set the framebuffer color depth? Where does the stm kernel driver get the format information? I can see from the driver that it checks which color format is used so how can I change this format?