I am experimenting with boot optimization on my Raspberry Pi 4 - Yocto based embedded Linux system and would like to set when vc4-drm kernel module is loaded.
I would like to make vc4-drm kernel module loaded earlier so that /dev/fb0 is ready earlier. Now, it exceeds my user space boot time, therefore I am not able to display anything on it for about 9 seconds. However, if I move it so that it is initialized earlier, I'm thinking it will be better.
Below is an image that shows major kernel modules that are loaded on my system, in a complete debug mode (bootchart+initcall_debug+serial+printk enabled). You will see that vc4_drm_register is almost at the end.
In order to approach the issue, I found these: What is the Linux built-in driver load order? and How does Linux determine the order of module init calls?. Yasushi Shoji states;
put your init function in the higher level, or put your device driver at the higher position in Makefile
For the first method, in the kernel that I'm compiling, I found the module in drivers/gpu/drm/vc4, then replaced module_init(vc4_drm_register) with both early_initcall(vc4_drm_register) and subsys_initcall(vc4_drm_register). Both attempts made absolutely no difference, vc4 still loads at around ~9th second. Either I'm missing something here, or this is being handled differently.
Second method suggested is to adjust the order in drivers/Makefile. However, to me gpu/ drivers seems already pretty early stage.
obj-y += irqchip/
obj-y += bus/
obj-$(CONFIG_GENERIC_PHY) += phy/
# GPIO must come after pinctrl as gpios may need to mux pins etc
obj-$(CONFIG_PINCTRL) += pinctrl/
obj-$(CONFIG_GPIOLIB) += gpio/
obj-y += pwm/
obj-y += pci/
obj-$(CONFIG_PARISC) += parisc/
obj-$(CONFIG_RAPIDIO) += rapidio/
obj-y += video/
obj-y += idle/
# IPMI must come before ACPI in order to provide IPMI opregion support
obj-y += char/ipmi/
obj-$(CONFIG_ACPI) += acpi/
obj-$(CONFIG_SFI) += sfi/
# PnP must come after ACPI since it will eventually need to check if acpi
# was used and do nothing if so
obj-$(CONFIG_PNP) += pnp/
obj-y += amba/
obj-y += clk/
# Many drivers will want to use DMA so this has to be made available
# really early.
obj-$(CONFIG_DMADEVICES) += dma/
# SOC specific infrastructure drivers.
obj-y += soc/
obj-$(CONFIG_VIRTIO) += virtio/
obj-$(CONFIG_XEN) += xen/
# regulators early, since some subsystems rely on them to initialize
obj-$(CONFIG_REGULATOR) += regulator/
# reset controllers early, since gpu drivers might rely on them to initialize
obj-$(CONFIG_RESET_CONTROLLER) += reset/
# tty/ comes before char/ so that the VT console is the boot-time
# default.
obj-y += tty/
obj-y += char/
# iommu/ comes before gpu as gpu are using iommu controllers
obj-$(CONFIG_IOMMU_SUPPORT) += iommu/
# gpu/ comes after char for AGP vs DRM startup and after iommu
obj-y += gpu/
# ...
# ...
# ...
# Continues with a lot more drivers here...
Therefore, I am in need of help to figure this out. How do I make sure that vc4 is loaded earlier than it is now? If I am missing anything, please let me know. Thank you very much.
NOTE: vc4-drm dmesg
root@raspberrypi4-64:~# dmesg | grep vc4
[ 9.123494] calling vc4_drm_register+0x0/0x1000 [vc4] @ 299
[ 9.184440] vc4-drm soc:gpu: bound fe600000.firmwarekms (ops vc4_fkms_ops [vc4])
[ 9.192810] [drm] Initialized vc4 0.0.0 20140616 for soc:gpu on minor 1
[ 9.380513] vc4-drm soc:gpu: fb0: DRM emulated frame buffer device
[ 9.393112] initcall vc4_drm_register+0x0/0x1000 [vc4] returned 0 after 187677 us
ecs
