This patch implements earlyprintk based on virtio console using early_wr config
register.
Kernel args for using this will be: earlyprintk=virtio-console,<phys_address>
Signed-off-by: Pranavkumar Sawargaonkar <pranavku...@linaro.org>
Signed-off-by: Anup Patel <anup.pa...@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..52ac6b0 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_EARLY_WRITE))) {
+ init_done = 1;
+ return;
+ }
+
+ init_done = 1;
+ can_write = 1;
+ }
+
+ if (can_write)
+ writeb_relaxed(ch, &p->early_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, },
{}
};
--
1.7.9.5
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