linux-kernel - Re: [PATCH 5/5] tty: amba-pl011: Add earlycon support for SBSA UART

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Date:   Mon, 24 Oct 2016 11:59:20 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Wei Xu <xuwei5@...ilicon.com>, Rob Herring <robh+dt@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, <majun258@...wei.com>,
        <guohanjun@...wei.com>, <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH 5/5] tty: amba-pl011: Add earlycon support for SBSA UART

Hi Greg, any more comments, thanks.

On 2016/9/27 21:15, Kefeng Wang wrote:
> 
> 
> On 2016/9/27 18:57, Greg Kroah-Hartman wrote:
>> On Sat, Sep 24, 2016 at 05:14:25PM +0800, Kefeng Wang wrote:
>>> Declare an OF early console for SBSA UART so that the early console device
>>> can be specified via the "stdout-path" property in device-tree.
>>>
>>> Cc: Russell King <linux@...linux.org.uk>
>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>>> ---
>>>  drivers/tty/serial/amba-pl011.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
>>> index 7d9b291..3688d3b 100644
>>> --- a/drivers/tty/serial/amba-pl011.c
>>> +++ b/drivers/tty/serial/amba-pl011.c
>>> @@ -2330,6 +2330,7 @@ static int __init pl011_early_console_setup(struct earlycon_device *device,
>>>  	return 0;
>>>  }
>>>  OF_EARLYCON_DECLARE(pl011, "arm,pl011", pl011_early_console_setup);
>>> +OF_EARLYCON_DECLARE(pl011, "arm,sbsa-uart", pl011_early_console_setup);
>>
>> Why do you need another option for the same thing?
> 
> 
> It is used to support earlycon(without option) for sbsa-uart in bootargs.
> 
> 	chosen {
> 		stdout-path = "serial0:115200n8";
> 		bootargs = "earlycon"
> 	};
> 
> 	uart0: uart@...b0000 {
> 		compatible = "arm,sbsa-uart";
> 		reg = <0x0 0x602b0000 0x0 0x1000>;
> 		...
> 	};
> 
> We setup a unique struct with compatible name by OF_EARLYCON_DECLARE,
> #define OF_EARLYCON_DECLARE(_name, compat, fn)				\
> 	static const struct earlycon_id __UNIQUE_ID(__earlycon_##_name)	\
> 	     __used __section(__earlycon_table)				\
> 		= { .name = __stringify(_name),				\
> 		    .compatible = compat,				\
> 		    .setup = fn  }
> 
> if without this patch(see drivers/of/fdt.c),
> 
> early_init_dt_scan_chosen_serial()
>  - for (match = __earlycon_table; match < __earlycon_table_end; match++)
>   -- if (fdt_node_check_compatible(fdt, offset, match->compatible))
> 	countinue;
>   -- of_setup_earlycon(match, offset, options); // will never touch here.
> 
> Thanks,
> Kefeng
> 
>>
>> confused,
>>
>> greg k-h
>>
>> .
>>
> 
> 
> .
>