On Wed, Apr 16, 2014 at 11:14:28PM +0100, Rob Herring wrote:
> On Mon, Mar 24, 2014 at 6:28 AM, Catalin Marinas
> <catalin.marinas@xxxxxxx> wrote:
> > On Fri, Mar 21, 2014 at 09:08:46PM +0000, Rob Herring wrote:
> >> From: Rob Herring <robh@xxxxxxxxxx>
> >>
> >> Add earlycon support for the pl011 serial port. This allows enabling
> >> the pl011 for console when early_params are processed. This is based
> >> on the arm64 earlyprintk support and is intended to replace it.
> >>
> >> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
> >> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> >> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> >> Cc: Jiri Slaby <jslaby@xxxxxxx>
> >> ---
> >> Documentation/kernel-parameters.txt | 5 +++--
> >> drivers/tty/serial/amba-pl011.c | 30 +++++++++++++++++++++++++++++-
> >> 2 files changed, 32 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> >> index 5ce8b7a..81bdd52 100644
> >> --- a/Documentation/kernel-parameters.txt
> >> +++ b/Documentation/kernel-parameters.txt
> >> @@ -887,8 +887,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> >> uart[8250],io,<addr>[,options]
> >> uart[8250],mmio,<addr>[,options]
> >> uart[8250],mmio32,<addr>[,options]
> >> - Start an early, polled-mode console on the 8250/16550
> >> - UART at the specified I/O port or MMIO address.
> >> + pl011,<addr>
> >> + Start an early, polled-mode console on a serial port
> >> + at the specified I/O port or MMIO address. 8250
> >> MMIO inter-register address stride is either 8-bit
> >> (mmio) or 32-bit (mmio32).
> >> The options are the same as for ttyS, above.
> >
> > I think the last line is a bit misleading. Or did you intend to leave it
> > with the uart[8250] parameter? See below:
>
> How about this (excuse the gmail lack of tabs):
>
> earlycon= [KNL] Output early console device and options.
>
> uart[8250],io,<addr>[,options]
> uart[8250],mmio,<addr>[,options]
> uart[8250],mmio32,<addr>[,options]
> Start an early, polled-mode console on an 8250 serial
> port at the specified I/O port or MMIO address. 8250
> MMIO inter-register address stride is either 8-bit
> (mmio) or 32-bit (mmio32).
>
> The options are the same as for ttyS, above.
>
> pl011,<addr>
> Start an early, polled-mode console on a pl011 serial
> port at the specified address. The pl011 serial port
> must already be setup and configured. Options are not
> yet supported.
>
> smh Use ARM semihosting calls for early console.
It looks fine.
> >> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> >> index d4eda24..4227c0a 100644
> >> --- a/drivers/tty/serial/amba-pl011.c
> >> +++ b/drivers/tty/serial/amba-pl011.c
> > [...]
> >> +static int __init pl011_early_console_setup(struct earlycon_device *device,
> >> + const char *opt)
> >> +{
> >> + if (!device->port.membase)
> >> + return -ENODEV;
> >> +
> >> + device->con->write = pl011_early_write;
> >> + return 0;
> >> +}
> >> +EARLYCON_DECLARE(pl011, pl011_early_console_setup);
> >
> > Here we expect the PL011 to be already initialised by the boot loader
> > and the kernel continues using the same settings. So maybe clarify this
> > in the pl011 kernel parameter doc and we can add proper configuration
> > using a separate patch.
>
> Enabling and setup would not be too hard, but either baud rate will
> always have to be configured or we'll have to specify the input clock
> rate too. The 8250 driver basically does the former or assumes a fixed
> clock.
>
> Adding any setup will also break any non-pl011 based SBSA compliant
> uart since the configuration registers are not standardized. I guess
> we can add "sbsauart" when/if that happens.
I think for now we can assume that the pl011 is initialised at the
right baud rate prior to starting the kernel.
--
Catalin
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
