How to use earlycon and earlyprintk on Samsung S3C24xx

[Woody Wu]

Tkanks a lot!

On Wednesday, March 2, 2016, <victorascroft at gmail.com> wrote:

> Hi,
>
> On 16-03-01 21:07:09, Woody Wu wrote:
> > On Friday, February 26, 2016, <victorascroft at gmail.com <javascript:;>>
> wrote:
> >
> > > Hi,
> > >
> > > On 16-02-26 00:55:40, Woody Wu wrote:
> > > > Hi,
> > > >
> > > > It seems, at least in 4.4.2 kernel, earlyprintk parameter supports
> > > > something like 's3c24xx,<addr>'. But I dont know where to find out
> the
> > > addr
> > > > value of the first uart port on my *s3c2416* based board.  Can
> someone
> > > > please tell me?
> > > >
> > > > Also, I desire to know if the earlycon parameter supports the Samsung
> > > > S3C24xx uarts, if so, what should the value of the parameter look
> like?
> > >
> > > Have a look in the documentation here
> > > https://www.kernel.org/doc/Documentation/kernel-parameters.txt
> > >
> > > The kernels kernel-parameter.txt documentation file lists the supported
> > > drivers.
> > >
> > > Generally the UART0 port is used for debugging but I guess there is
> > > no such hard and fast rule.
> > >
> > > For your particular board, you can check which UART port is used
> > > as the debug serial console and then get the address for the concerned
> > > UART by checking the relevant dtsi file in
> > > arch/arm/boot/dts/s3c24xx.dtsi or perhaps one of the exynosX.dtsi
> files?
> > >
> > > UART0 port seems to have address of 0x50000000?
> > >
> > > Regards,
> > > Sanchayan.
> >
> >
> > Thanks for you pointing me to the dtsi files, very informational ! And,
> > yes, the uart0 address os 0x50000000 and I has made it work via
> > 'earlyprintk=serial,0x50000000,115200'.  By the way, is this a physical
> > address or mmap-ed address?
>
> The addresses specified in the DTS files are always physical addresses. So
> 0x50000000 is a physical address. This address will be mapped using one of
> the ioremap calls by the driver and used further by kernel using
> readl/writel
> calls.
>
> You can see the earlycon support declaration here
> http://lxr.free-electrons.com/source/drivers/tty/serial/samsung.c#L2452
>
> s3c24xx_serial_probe
> -->s3c24xx_serial_init_port
> ---->Call to devm_ioremap
>
> http://lxr.free-electrons.com/source/drivers/tty/serial/samsung.c#L1705
>
> - Sanchayan.
>
>
> >
> > >
> > > >
> > > > Thank in advance,
> > > >
> > > > -woody
> > > >
> > > >
> > > > --
> > > > Life is the only flaw in an otherwise perfect nonexistence
> > > >     -- Schopenhauer
> > > >
> > > > woody
> > > > public key at http://subkeys.pgp.net:11371 (narkewoody at gmail.com
> <javascript:;>
> > > <javascript:;>)
> > >
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> > >
> >
> > --
> > Life is the only flaw in an otherwise perfect nonexistence
> >     -- Schopenhauer
> >
> > woody
> > public key at http://subkeys.pgp.net:11371 (narkewoody at gmail.com
> <javascript:;>)
>


-- 
Life is the only flaw in an otherwise perfect nonexistence
    -- Schopenhauer

woody
public key at http://subkeys.pgp.net:11371 (narkewoody at gmail.com)
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