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?