linux-kernel - Re: [PATCH v3 4/4] x86, earlyprintk: add hsu early console for Intel Medfield platform

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Message-ID: <20100921162627.GA21459@dumpdata.com>
Date:	Tue, 21 Sep 2010 12:26:27 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Feng Tang <feng.tang@...el.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, alan@...ux.intel.com,
	greg@...ah.com, x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH v3 4/4] x86, earlyprintk: add hsu early console for
 Intel Medfield platform

On Mon, Sep 13, 2010 at 03:08:56PM +0800, Feng Tang wrote:
> Intel Medfield platform has a high speed UART device, which could act
> as a early console. To enable early printk of HSU console, simply add
> "earlyprintk=hsu" in kernel command line.
> 
> Currently we put the code in the early_printk_mrst.c as it is also for
> Intel MID platforms like the mrst early console
> 
> Signed-off-by: Feng Tang <feng.tang@...el.com>
> Cc: x86 maintainers <x86@...nel.org>
> Signed-off-by: Alan Cox <alan@...ux.intel.com>
> ---
>  arch/x86/include/asm/mrst.h         |    3 +
>  arch/x86/kernel/early_printk.c      |    6 ++
>  arch/x86/kernel/early_printk_mrst.c |   89 ++++++++++++++++++++++++++++++++++-
>  3 files changed, 97 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/include/asm/mrst.h b/arch/x86/include/asm/mrst.h
> index d0ea5bc..4a711a6 100644
> --- a/arch/x86/include/asm/mrst.h
> +++ b/arch/x86/include/asm/mrst.h
> @@ -47,4 +47,7 @@ extern enum mrst_timer_options mrst_timer_options;
>  
>  extern struct console early_mrst_console;
>  extern void mrst_early_console_init(void);
> +
> +extern struct console early_hsu_console;
> +extern void hsu_early_console_init(void);
>  #endif /* _ASM_X86_MRST_H */
> diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
> index 6082463..4572f25 100644
> --- a/arch/x86/kernel/early_printk.c
> +++ b/arch/x86/kernel/early_printk.c
> @@ -245,6 +245,12 @@ static int __init setup_early_printk(char *buf)
>  			mrst_early_console_init();
>  			early_console_register(&early_mrst_console, keep);
>  		}
> +
> +		if (!strncmp(buf, "hsu", 3)) {
> +			hsu_early_console_init();
> +			early_console_register(&early_hsu_console, keep);
> +		}
> +
>  #endif
>  		buf++;
>  	}
> diff --git a/arch/x86/kernel/early_printk_mrst.c b/arch/x86/kernel/early_printk_mrst.c
> index 05d27e1..65df603 100644
> --- a/arch/x86/kernel/early_printk_mrst.c
> +++ b/arch/x86/kernel/early_printk_mrst.c
> @@ -1,5 +1,5 @@
>  /*
> - * early_printk_mrst.c - spi-uart early printk for Intel Moorestown platform
> + * early_printk_mrst.c - early consoles for Intel MID platforms
>   *
>   * Copyright (c) 2008-2010, Intel Corporation
>   *
> @@ -9,9 +9,19 @@
>   * of the License.
>   */
>  
> +/*
> + * This file implements two early consoles named mrst and hsu.
> + * mrst is based on Maxim3110 spi-uart device, it exists in both
> + * Moorestown and Medfield platforms, while hsu is based on a High
> + * Speed UART device which only exists in the Medfield platform
> + */
> +
> +#include <linux/serial_reg.h>
> +#include <linux/serial_mfd.h>
>  #include <linux/kmsg_dump.h>
>  #include <linux/console.h>
>  #include <linux/kernel.h>
> +#include <linux/delay.h>
>  #include <linux/init.h>
>  #include <linux/io.h>
>  
> @@ -230,3 +240,80 @@ struct console early_mrst_console = {
>  	.flags =	CON_PRINTBUFFER,
>  	.index =	-1,
>  };
> +
> +/*
> + * Following is the early console based on Medfield HSU (High
> + * Speed UART) device.

Is there a link to a PDF of the device in question?

> + */
> +#define HSU_PORT2_PADDR		0xffa28180

Is it _always_ that address?
> +
> +static void __iomem *phsu;
> +
> +void hsu_early_console_init(void)
> +{
> +	u8 lcr;
> +
> +	phsu = (void *)set_fixmap_offset_nocache(FIX_EARLYCON_MEM_BASE,
> +							HSU_PORT2_PADDR);
> +
> +	/* Disable FIFO */
> +	writeb(0x0, phsu + UART_FCR);

No detection? What happens if you don't have the device (say in production it gets removed)
and we try to use earlyprintk=hsu? Won't we have some trouble?

> +
> +	/* Set to default 115200 bps, 8n1 */

Is that OK? Should there be some parsing of the baudrate data?
> +	lcr = readb(phsu + UART_LCR);
> +	writeb((0x80 | lcr), phsu + UART_LCR);
> +	writeb(0x18, phsu + UART_DLL);
> +	writeb(lcr,  phsu + UART_LCR);
> +	writel(0x3600, phsu + UART_MUL*4);
--
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