This patch-set implements early printk support for virtio console devices without using any hypercalls.
The current virtio early printk code in kernel expects that hypervisor will provide some mechanism generally a hypercall to support early printk. This patch-set does not break existing hypercall based early print support.
This implementation adds: 1. Early writeonly register named early_wr in virtio console's config space. 2. Host feature flags namely VIRTIO_CONSOLE_F_EARLY_WRITE for telling guest about early-write capability in console device.
Early write mechanism: 1. When a guest wants to out some character, it has to simply write the character to early_wr register in config space of virtio console device.
Pranavkumar Sawargaonkar (2): virtio: console: Add early writeonly register to config space arm64: earlyprintk support for virtio-mmio console
Documentation/virtual/virtio-spec.txt | 13 ++++++++++-- arch/arm64/kernel/early_printk.c | 35 +++++++++++++++++++++++++++++++++ include/uapi/linux/virtio_console.h | 3 +++ 3 files changed, 49 insertions(+), 2 deletions(-)