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arm64: add support for 8250/16550 earlyprintk

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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,<phys_address>

Kernel args for 32-bit aligned regs: earlyprintk=uart8250-32bit,<phys_address>

Signed-off-by: Anup Patel <anup.patel@linaro.org>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Anup Patel 2013-03-01 08:41:47 +00:00 committed by Catalin Marinas
parent 0492f72508
commit e53f2f4b57
1 changed files with 23 additions and 0 deletions
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23
arch/arm64/kernel/early_printk.c
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@ -24,6 +24,7 @@
#include <linux/io.h>
#include <linux/amba/serial.h>
#include <linux/serial_reg.h>
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, },
{}
};