On Thu, Apr 25, 2024 at 12:50:12PM GMT, Daniel Henrique Barboza wrote: > SBI defines a Debug Console extension "DBCN" that will, in time, replace > the legacy console putchar and getchar SBI extensions. > > The appeal of the DBCN extension is that it allows multiple bytes to be > read/written in the SBI console in a single SBI call. > > As far as KVM goes, the DBCN calls are forwarded by an in-kernel KVM > module to userspace. But this will only happens if the KVM module > actually supports this SBI extension and we activate it. > > We'll check for DBCN support during init time, checking if get-reg-list > is advertising KVM_RISCV_SBI_EXT_DBCN. In that case, we'll enable it via > kvm_set_one_reg() during kvm_arch_init_vcpu(). > > Finally, change kvm_riscv_handle_sbi() to handle the incoming calls for > SBI_EXT_DBCN, reading and writing as required. > > A simple KVM guest with 'earlycon=sbi', running in an emulated RISC-V > host, takes around 20 seconds to boot without using DBCN. With this > patch we're taking around 14 seconds to boot due to the speed-up in the > terminal output. There's no change in boot time if the guest isn't > using earlycon. > > Signed-off-by: Daniel Henrique Barboza <[email protected]> > --- > target/riscv/kvm/kvm-cpu.c | 111 +++++++++++++++++++++++++++++ > target/riscv/sbi_ecall_interface.h | 17 +++++ > 2 files changed, 128 insertions(+) >
Reviewed-by: Andrew Jones <[email protected]>
