linux-kernel - Re: [PATCH v2 5/5] tty/serial: Add earlycon support for Spreadtrum serial driver

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Date:	Mon, 20 Oct 2014 19:15:15 +0800
From:	Lyra Zhang <zhang.lyra@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"jslaby@...e.cz" <jslaby@...e.cz>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"broonie@...aro.org" <broonie@...aro.org>,
	"m-karicheri2@...com" <m-karicheri2@...com>,
	Pawel Moll <Pawel.Moll@....com>,
	"artagnon@...il.com" <artagnon@...il.com>,
	"rrichter@...ium.com" <rrichter@...ium.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Will Deacon <Will.Deacon@....com>,
	"orsonzhai@...il.com" <orsonzhai@...il.com>,
	"geng.ren@...eadtrum.com" <geng.ren@...eadtrum.com>,
	"zhizhou.zhang@...eadtrum.com" <zhizhou.zhang@...eadtrum.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"sprdlinux@...elists.org" <sprdlinux@...elists.org>
Subject: Re: [PATCH v2 5/5] tty/serial: Add earlycon support for Spreadtrum
 serial driver

2014-10-20 18:32 GMT+08:00 Mark Rutland <mark.rutland@....com>:
> On Mon, Oct 20, 2014 at 08:27:24AM +0100, Lyra Zhang wrote:
>> 2014-10-17 21:03 GMT+08:00 Mark Rutland <mark.rutland@....com>:
>> > On Fri, Oct 17, 2014 at 10:54:25AM +0100, Chunyan Zhang wrote:
>> >> Add serial driver for spreadtrum sharkl platform with earlycon
>> >> support at first.
>> >>
>> >> Signed-off-by: Chunyan Zhang <chunyan.zhang@...eadtrum.com>
>> >> ---
>> >>  drivers/tty/serial/Kconfig       |   24 ++++++++++++++
>> >>  drivers/tty/serial/Makefile      |    1 +
>> >>  drivers/tty/serial/sprd-serial.c |   64 ++++++++++++++++++++++++++++++++++++++
>> >>  3 files changed, 89 insertions(+)
>> >>  create mode 100644 drivers/tty/serial/sprd-serial.c
>> >>
>> >> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
>> >> index 26cec64..33b8f90 100644
>> >> --- a/drivers/tty/serial/Kconfig
>> >> +++ b/drivers/tty/serial/Kconfig
>> >> @@ -113,6 +113,30 @@ config SERIAL_SB1250_DUART_CONSOLE
>> >>
>> >>         If unsure, say Y.
>> >>
>> >> +config SERIAL_SPRD
>> >> +     tristate "Support for SPRD serial"
>> >> +     depends on ARM || ARM64
>> >> +     select SERIAL_CORE
>> >> +     help
>> >> +          This enables the driver for the Spreadtrum's serial.
>> >> +
>> >> +config SERIAL_SPRD_NR
>> >> +        int "Maximum number of sprd serial ports"
>> >> +        depends on SERIAL_SPRD
>> >> +        default "4"
>> >
>> > This is not used below.
>> >
>> Ok, I'll remove it in v3.
>>
>> >> +
>> >> +config SERIAL_SPRD_CONSOLE
>> >> +        bool "SPRD UART console support"
>> >> +        depends on SERIAL_SPRD=y
>> >> +        select SERIAL_CORE_CONSOLE
>> >> +     select SERIAL_EARLYCON
>> >> +        help
>> >> +       Support for early debug console using Spreadtrum's serial. This enables
>> >> +       the console before standard serial driver is probed. This is enabled
>> >> +       with "earlycon=serial_sprd" on the kernel command line. The console is
>> >> +       enabled when early_param is processed.
>> >
>> > There only appears to be an earlycon driver, and not "standard serial
>> > driver".
>> >
>> > What happens after earlycon?
>> >
>> > Surely there should be a real driver to take ownership of the UART?
>> >
>> > As far as I can see it won't be possible to boot your platform to a
>> > prompt, because earlycon will have gone before that.
>> >
>> > Thanks,
>> > Mark.
>> >
>>
>> We are planed to add standard serial driver after this patch-set is approved.
>> In the first patch we contribute to the upstream, I'd like to add
>> architecture related code of
>> Spreadtrum's Sharkl, and then we will add more functions about Sharkl3
>> SoC step by step.
>
> The series is simple enough that the only issues I've noticed are minor.
> I'm happy with that.
>
> However, the absence of a real UART driver means that this series alone
> is not sufficient to boot your platform to a usable state. Given that
> the rest of the series is simply plumbing, I think it would make sense
> for that to accompany a full UART driver (or perhaps some other I/O like
> ethernet) such that it's possible to interact with the platform.
>
Ok, I see. I'll add a full UART driver in v3.
Thanks for your suggestion.

Best regards,
Chunyan
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