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

Konrad Rzeszutek Wilk
2010-09-21T16:29:27Z

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@intel.com>
> Cc: x86 maintainers <x86@kernel.org>
> Signed-off-by: Alan Cox <alan@linux.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);