2014-04-16 22:14:31

by Rob Herring

[permalink] [raw]
Subject: Re: [PATCH 6/8] tty/serial: pl011: add generic earlycon support

On Mon, Mar 24, 2014 at 6:28 AM, Catalin Marinas
<[email protected]> wrote:
> On Fri, Mar 21, 2014 at 09:08:46PM +0000, Rob Herring wrote:
>> From: Rob Herring <[email protected]>
>>
>> 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 <[email protected]>
>> Cc: Russell King <[email protected]>
>> Cc: Greg Kroah-Hartman <[email protected]>
>> Cc: Jiri Slaby <[email protected]>
>> ---
>> 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.


>
>> 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.

Rob


2014-04-23 16:40:17

by Catalin Marinas

[permalink] [raw]
Subject: Re: [PATCH 6/8] tty/serial: pl011: add generic earlycon support

On Wed, Apr 16, 2014 at 11:14:28PM +0100, Rob Herring wrote:
> On Mon, Mar 24, 2014 at 6:28 AM, Catalin Marinas
> <[email protected]> wrote:
> > On Fri, Mar 21, 2014 at 09:08:46PM +0000, Rob Herring wrote:
> >> From: Rob Herring <[email protected]>
> >>
> >> 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 <[email protected]>
> >> Cc: Russell King <[email protected]>
> >> Cc: Greg Kroah-Hartman <[email protected]>
> >> Cc: Jiri Slaby <[email protected]>
> >> ---
> >> 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