linux-kernel - Re: [PATCH v2 1/3] serial: earlycon-arm-semihost: Move smh_putc() variants in respective arch's semihost.h

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Message-Id: <em14380c7e-ee2b-45d5-8879-dde687f03b2b@eea79fc7.com>
Date:   Thu, 08 Dec 2022 09:32:48 +0000
From:   "Bin Meng" <bmeng@...ylab.org>
To:     "Jiri Slaby" <jirislaby@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-serial <linux-serial@...r.kernel.org>
Cc:     "catalin.marinas" <catalin.marinas@....com>,
        gregkh <gregkh@...uxfoundation.org>,
        linux <linux@...linux.org.uk>, will <will@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/3] serial: earlycon-arm-semihost: Move smh_putc() variants in
 respective arch's semihost.h

On 2022/12/8 14:08:33, "Jiri Slaby" <jirislaby@...nel.org> wrote:

>On 07. 12. 22, 14:53, Bin Meng wrote:
>>Move smh_putc() variants in respective arch/*/include/asm/semihost.h,
>>in preparation to add RISC-V support.
>>
>>Signed-off-by: Bin Meng <bmeng@...ylab.org>
>...
>>--- /dev/null
>>+++ b/arch/arm/include/asm/semihost.h
>>@@ -0,0 +1,23 @@
>>+/* SPDX-License-Identifier: GPL-2.0 */
>>+/*
>>+ * Copyright (C) 2012 ARM Ltd.
>>+ * Author: Marc Zyngier <marc.zyngier@....com>
>>+ *
>>+ * Adapted for ARM and earlycon:
>>+ * Copyright (C) 2014 Linaro Ltd.
>>+ * Author: Rob Herring <robh@...nel.org>
>>+ */
>
>Much better. There are three minor issues:
>1) protection against multiple #include-s is missing here.

Oops, will add in v3.

>
>
>>+#ifdef CONFIG_THUMB2_KERNEL
>>+#define SEMIHOST_SWI	"0xab"
>>+#else
>>+#define SEMIHOST_SWI	"0x123456"
>>+#endif
>>+
>>+static inline void smh_putc(struct uart_port *port, unsigned char c)
>
>2) port is unused in all implementations. So it should be dropped.
>3) can you make "c" an explicit u8?

The smh_putc function signature is defined by the uart_console_write 
helper. I don't think we can change it.

>
>>+{
>>+	asm volatile("mov  r1, %0\n"
>>+		     "mov  r0, #3\n"
>>+		     "svc  " SEMIHOST_SWI "\n"
>>+		     : : "r" (&c) : "r0", "r1", "memory");
>>+}

Regards,
Bin