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: Anup Patel <anup.patel@linaro.org> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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@ -24,6 +24,7 @@
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#include <linux/io.h>
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#include <linux/amba/serial.h>
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#include <linux/serial_reg.h>
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static void __iomem *early_base;
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static void (*printch)(char ch);
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@ -51,6 +52,26 @@ static void smh_printch(char ch)
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: : "r" (&ch) : "x0", "x1", "memory");
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}
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/*
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* 8250/16550 (8-bit aligned registers) single character TX.
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*/
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static void uart8250_8bit_printch(char ch)
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{
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while (!(readb_relaxed(early_base + UART_LSR) & UART_LSR_THRE))
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;
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writeb_relaxed(ch, early_base + UART_TX);
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}
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/*
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* 8250/16550 (32-bit aligned registers) single character TX.
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*/
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static void uart8250_32bit_printch(char ch)
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{
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while (!(readl_relaxed(early_base + (UART_LSR << 2)) & UART_LSR_THRE))
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;
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writel_relaxed(ch, early_base + (UART_TX << 2));
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}
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struct earlycon_match {
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const char *name;
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void (*printch)(char ch);
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@ -59,6 +80,8 @@ struct earlycon_match {
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static const struct earlycon_match earlycon_match[] __initconst = {
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{ .name = "pl011", .printch = pl011_printch, },
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{ .name = "smh", .printch = smh_printch, },
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{ .name = "uart8250-8bit", .printch = uart8250_8bit_printch, },
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{ .name = "uart8250-32bit", .printch = uart8250_32bit_printch, },
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{}
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};
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