From e53f2f4b570d85c7208dfc97de54db1296b88207 Mon Sep 17 00:00:00 2001 From: Anup Patel Date: Fri, 1 Mar 2013 08:41:47 +0000 Subject: [PATCH] arm64: add support for 8250/16550 earlyprintk This patch adds support for using earlyprintk with 8250/16550 UART ports. The 8250/16550 UART can either have 8-bit or 32-bit aligned registers which is HW vendor dependent. Kernel args for 8-bit aligned regs: earlyprintk=uart8250-8bit, Kernel args for 32-bit aligned regs: earlyprintk=uart8250-32bit, Signed-off-by: Anup Patel Reviewed-by: Marc Zyngier Signed-off-by: Catalin Marinas --- arch/arm64/kernel/early_printk.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/arch/arm64/kernel/early_printk.c b/arch/arm64/kernel/early_printk.c index 0bb7436c57dc..ac974f48a7a2 100644 --- a/arch/arm64/kernel/early_printk.c +++ b/arch/arm64/kernel/early_printk.c @@ -24,6 +24,7 @@ #include #include +#include static void __iomem *early_base; static void (*printch)(char ch); @@ -51,6 +52,26 @@ static void smh_printch(char ch) : : "r" (&ch) : "x0", "x1", "memory"); } +/* + * 8250/16550 (8-bit aligned registers) single character TX. + */ +static void uart8250_8bit_printch(char ch) +{ + while (!(readb_relaxed(early_base + UART_LSR) & UART_LSR_THRE)) + ; + writeb_relaxed(ch, early_base + UART_TX); +} + +/* + * 8250/16550 (32-bit aligned registers) single character TX. + */ +static void uart8250_32bit_printch(char ch) +{ + while (!(readl_relaxed(early_base + (UART_LSR << 2)) & UART_LSR_THRE)) + ; + writel_relaxed(ch, early_base + (UART_TX << 2)); +} + struct earlycon_match { const char *name; void (*printch)(char ch); @@ -59,6 +80,8 @@ struct earlycon_match { static const struct earlycon_match earlycon_match[] __initconst = { { .name = "pl011", .printch = pl011_printch, }, { .name = "smh", .printch = smh_printch, }, + { .name = "uart8250-8bit", .printch = uart8250_8bit_printch, }, + { .name = "uart8250-32bit", .printch = uart8250_32bit_printch, }, {} }; -- 2.20.1