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Commit e53f2f4b authored by Anup Patel's avatar Anup Patel Committed by Catalin Marinas
Browse files

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,<phys_address>

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

Signed-off-by: default avatarAnup Patel <anup.patel@linaro.org>
Reviewed-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 0492f725

arch/arm64/kernel/early_printk.c

+23 −0
Original line number Diff line number Diff line
@@ -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, },

	{}

};