release: 32-bit ubuntu 20.04 running on a raspberry pi 4
package: linux-raspi 5.4.0.1008.8
I made the configuration change described in:
https://bugs.launchpad.net/ubuntu/+source/linux-raspi/+bug/1876862
and am running a kernel with v3d on a raspberry pi 4.
Unfortunately, OpenGL is still not using the GPU; it's using the software renderer, llvmpipe.
Setting LIBGL_DEBUG=verbose and running an OpenGL program shows that OpenGL can't open any /dev/dri/renderD* device.
Looking in /dev/dri, there are no device files that begin with "render," indicating the v3d driver isn't starting up properly.
Adding debugging code to the kernel, I find that:
(1) drivers/gpu/drm/v3d/v3d_drv.c:v3d_platform_drm_probe() fails because it can't get a clock - devm_clk_get() returns an error.
(2) in drivers/clk/clk.c:of_clk_get_hw(), the call to of_parse_clkspec() for the v3d driver yields a desired clock source of "firmware-clocks".
(3) drivers/clk/clk.c:of_clk_get_hw_from_clkspec() fails because it can only find six clock providers (aux@7e215000, cprman@7e101000, clock@7ef00000, clk-108M, clk-usb, clk-osc) none of which match the requested "firmware-clocks".
The solution is to add a clock definition to the kernel source and a corresponding change to the device tree, but I'm not familiar enough with either to create that solution myself.
In the raspbian kernel source tree, drivers/clk/bcm/clk-raspberrypi.c defines BCM2835_CLOCK_V3D, but there is no corresponding definition in the ubuntu source tree.
i forgot to mention: the relevant device tree file is:
arch/