linux-kernel - Re: [PATCH] tty/serial: samsung: Add earlycon support

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Date:	Sat, 20 Sep 2014 13:00:15 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Tomasz Figa <tomasz.figa@...il.com>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	gregkh@...uxfoundation.org
CC:	linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Rob Herring <robh@...nel.org>, thomas.ab@...sung.com,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] tty/serial: samsung: Add earlycon support

On 09/20/2014 08:39 AM, Tomasz Figa wrote:
> Hi Alim,
> 
> Please see my comments inline.
> 
> On 16.09.2014 13:32, Alim Akhtar wrote:
>> Add earlycon support for the samsung serial port. This allows enabling
>> the samsung serial port for console when early_params are parse and processed.
>>
>> Signed-off-by: Alim Akhtar <alim.akhtar@...sung.com>
>> ---
>>  Documentation/kernel-parameters.txt |    6 ++++++
>>  drivers/tty/serial/Kconfig          |    1 +
>>  drivers/tty/serial/samsung.c        |   17 +++++++++++++++++
>>  3 files changed, 24 insertions(+)
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index 5ae8608..e01c0e5 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -936,6 +936,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>  			must already be setup and configured. Options are not
>>  			yet supported.
>>  
>> +		samsung,<addr>

There will only ever be 1 samsung uart? This is an ABI to some extent,
so you will be stuck with it.

>> +			Start an early, polled-mode console on a samsung serial
>> +			port at the specified address. The samsung serial port
>> +			must already be setup and configured. Options are not
>> +			yet supported.
>> +
> 
> Couldn't you simply parse this from DT? I believe there is already code
> parsing stdout property in chosen node for earlycon purposes present in
> the kernel.

You should support both and it is just a OF_EARLYCON_DECLARE line to add.

> Anyway, we already had a patch for this in our internal tree, but it
> wasn't submitted because there was no support for early ioremap on ARM
> at that time. I haven't been following it since then (and I'm no longer
> at Samsung; Marek might be able to take this topic), is it already
> available?

No, but should be soonish. fixmap parts are being worked on by Kees.

Rob

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