arm64: add support for MSM HSL earlyprintk

Add support for arm64 earlyprintk using the MSM UARTDM
hardware block. Such support can be enabled by passing
something like "earlyprintk=msm_hsl_uart,0xf991e000" (or
the appropriate equivalent) on the kernel command line.

Change-Id: Ia43ad430e8bdcb0fd724c60949b82b256e2611a8
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/arch/arm64/kernel/early_printk.c b/arch/arm64/kernel/early_printk.c
index fbb6e184365..1263337a1e8 100644
--- a/arch/arm64/kernel/early_printk.c
+++ b/arch/arm64/kernel/early_printk.c
@@ -72,6 +72,28 @@ static void uart8250_32bit_printch(char ch)
 	writel_relaxed(ch, early_base + (UART_TX << 2));
 }
 
+#define MSM_HSL_UART_SR			0xa4
+#define MSM_HSL_UART_ISR		0xb4
+#define MSM_HSL_UART_TF			0x100
+#define MSM_HSL_UART_CR			0xa8
+#define MSM_HSL_UART_NCF_TX		0x40
+#define MSM_HSL_UART_SR_TXEMT		BIT(3)
+#define MSM_HSL_UART_ISR_TXREADY	BIT(7)
+
+void msm_hsl_uart_printch(char ch)
+{
+	while (!(readl_relaxed(early_base + MSM_HSL_UART_SR) &
+						       MSM_HSL_UART_SR_TXEMT) &&
+	       !(readl_relaxed(early_base + MSM_HSL_UART_ISR) &
+						     MSM_HSL_UART_ISR_TXREADY))
+		;
+
+	writel_relaxed(0x300, early_base + MSM_HSL_UART_CR);
+	writel_relaxed(1, early_base + MSM_HSL_UART_NCF_TX);
+	readl_relaxed(early_base + MSM_HSL_UART_NCF_TX);
+	writel_relaxed(ch, early_base + MSM_HSL_UART_TF);
+}
+
 struct earlycon_match {
 	const char *name;
 	void (*printch)(char ch);
@@ -82,6 +104,7 @@ 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 = "msm_hsl_uart", .printch = msm_hsl_uart_printch, },
 	{}
 };