Re: [PATCH v3] earlycon: 8250: Fix command line regression

Peter Hurley
2015-04-04T16:23:27Z

On 04/04/2015 12:09 PM, Greg Kroah-Hartman wrote:
> On Sat, Apr 04, 2015 at 10:27:30AM -0400, Peter Hurley wrote:
>> Restore undocumented behavior of kernel command line parameters of
>> the forms:
>> console=uart[8250],io|mmio|mmio32,<addr>[,options]
>> console=uart[8250],<addr>[,options]
>> where 'options' have not been specified; in this case, the hardware
>> is assumed to be initialized.
>>
>> Document the required behavior of the original implementation.
>>
>> Fixes: c7cef0a84912cab3c9df8 ("console: Add extensible console matching")
>> Reported-by: Yinghai Lu <yinghai@kernel.org>
>> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
>> ---
>>
>> v3: Fixed automatic console to port line settings initialization;
>> open-coded serial8250_console_setup() so the baud can be probed;
>> added sha reference in commit log
>>
>> v2: Fixed regression which allowed "console=uart1337,..." to start a
>> console (but not an earlycon)
>> + fixed earlycon= documentation related required behavior fixed by
>> this patch
>>
>> Documentation/kernel-parameters.txt | 18 ++++++++++++++---
>> drivers/tty/serial/8250/8250_core.c | 38 +++++++++++++++++++++++++++++++++---
>> drivers/tty/serial/8250/8250_early.c | 19 ------------------
>> 3 files changed, 50 insertions(+), 25 deletions(-)
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index bfcb1a6..1facf0b 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -713,10 +713,18 @@ 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]
>> + uart[8250],0x<addr>[,options]
>> Start an early, polled-mode console on the 8250/16550
>> UART at the specified I/O port or MMIO address,
>> - switching to the matching ttyS device later. The
>> - options are the same as for ttyS, above.
>> + switching to the matching ttyS device later.
>> + MMIO inter-register address stride is either 8-bit
>> + (mmio) or 32-bit (mmio32).
>> + If none of [io|mmio|mmio32], <addr> is assumed to be
>> + equivalent to 'mmio'. 'options' are specified in the
>> + same format described for ttyS above; if unspecified,
>> + the h/w is not re-initialized.
>> +
>> hvc<n> Use the hypervisor console device <n>. This is for
>> both Xen and PowerPC hypervisors.
>>
>> @@ -944,11 +952,15 @@ 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]
>> + uart[8250],0x<addr>[,options]
>> Start an early, polled-mode console on the 8250/16550
>> UART at the specified I/O port or MMIO address.
>> MMIO inter-register address stride is either 8-bit
>> (mmio) or 32-bit (mmio32).
>> - The options are the same as for ttyS, above.
>> + If none of [io|mmio|mmio32], <addr> is assumed to be
>> + equivalent to 'mmio'. 'options' are specified in the
>> + same format described for "console=ttyS<n>"; if
>> + unspecified, the h/w is not initialized.
>>
>> pl011,<addr>
>> Start an early, polled-mode console on a pl011 serial
>> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
>> index e0fb5f0..f59c7a0 100644
>> --- a/drivers/tty/serial/8250/8250_core.c
>> +++ b/drivers/tty/serial/8250/8250_core.c
>> @@ -3447,6 +3447,22 @@ static int univ8250_console_setup(struct console *co, char *options)
>> return serial8250_console_setup(up, options);
>> }
>>
>> +/* FIXME: this is broken on most other 8250 h/w */
>
> What do you mean by "most other"? What hardware does this work for?
> What is it broken for? What is someone supposed to think/do with this
> comment?

It's a direct copy of the existing behavior for 8250 earlycon, which is
broken for h/w with non-standard divisor registers. That's basically
_every_ new design, because that's what vendors need to extend to support
modern bitrates.

Affected h/w that I know of includes: 8250_dw, exar xr17v35 cards, omap8250,
omap15xx, intel byt, intel mid.

But it was already broken for these and so not a regression.

Regards,
Peter Hurley