This patch implements earlyprintk based on virtio console using emerg_wr config register.
Kernel args for using this will be: earlyprintk=virtio-console,<phys_address>
Signed-off-by: Pranavkumar Sawargaonkar pranavkumar@linaro.org Signed-off-by: Anup Patel anup.patel@linaro.org --- arch/arm64/kernel/early_printk.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+)
diff --git a/arch/arm64/kernel/early_printk.c b/arch/arm64/kernel/early_printk.c index ac974f4..ea3d2f5 100644 --- a/arch/arm64/kernel/early_printk.c +++ b/arch/arm64/kernel/early_printk.c @@ -25,6 +25,9 @@
#include <linux/amba/serial.h> #include <linux/serial_reg.h> +#include <linux/virtio_ids.h> +#include <linux/virtio_mmio.h> +#include <linux/virtio_console.h>
static void __iomem *early_base; static void (*printch)(char ch); @@ -53,6 +56,37 @@ static void smh_printch(char ch) }
/* + * VIRTIO MMIO console single character Tx. + */ +static void virtio_console_printch(char ch) +{ + u32 tmp; + static u32 init_done; + static u32 can_write; + struct virtio_console_config *p = early_base + VIRTIO_MMIO_CONFIG; + + if (!init_done) { + tmp = readl_relaxed(early_base + VIRTIO_MMIO_DEVICE_ID); + if (tmp != VIRTIO_ID_CONSOLE) { + init_done = 1; + return; + } + + tmp = readl_relaxed(early_base + VIRTIO_MMIO_HOST_FEATURES); + if (!(tmp & (1 << VIRTIO_CONSOLE_F_EMERG_WRITE))) { + init_done = 1; + return; + } + + init_done = 1; + can_write = 1; + } + + if (can_write) + writeb_relaxed(ch, &p->emerg_wr); +} + +/* * 8250/16550 (8-bit aligned registers) single character TX. */ static void uart8250_8bit_printch(char ch) @@ -82,6 +116,7 @@ static const struct earlycon_match earlycon_match[] __initconst = { { .name = "smh", .printch = smh_printch, }, { .name = "uart8250-8bit", .printch = uart8250_8bit_printch, }, { .name = "uart8250-32bit", .printch = uart8250_32bit_printch, }, + { .name = "virtio-console", .printch = virtio_console_printch, }, {} };