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 11:32:13 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Lyra Zhang <zhang.lyra@...il.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

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.

Thanks,
Mark.
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