linux-kernel - Re: [PATCH v3 -next 11/11] serial: 8250_early: Remove setup_early_serial8250

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Message-ID: <CAE9FiQXaOZOf4hj72iUpDoYgGTuO+jwF34qOeiLw=3rrWK+ucA@mail.gmail.com>
Date:	Fri, 3 Apr 2015 09:57:56 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Peter Hurley <peter@...leysoftware.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, Rob Herring <robh@...nel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v3 -next 11/11] serial: 8250_early: Remove setup_early_serial8250_console()

On Fri, Apr 3, 2015 at 3:37 AM, Peter Hurley <peter@...leysoftware.com> wrote:
> On 04/02/2015 10:38 PM, Yinghai Lu wrote:
>> On Thu, Apr 2, 2015 at 5:22 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>
>>>>>> still have another problem.
>>>>>> when using console=uart8250,io,0x3f8
>>>>>> it works as earlycon at first.
>>>>>> but after handover to normal console
>>>>>> it will revert back to 9600 again.
>>>>>
>>>>> this regression should be caused by:
>>>>>
>>>>> commit c7cef0a84912cab3c9df8949b034e4aa62982ec9
>>>>> Author: Peter Hurley <peter@...leysoftware.com>
>>>>> Date:   Mon Mar 9 16:27:12 2015 -0400
>>>>>
>>>>>     console: Add extensible console matching
>>>>
>>> So your whole patchset will need the first patch ?
>>>
>>> or can you just drop the first one patch ?
>>
>> Please check attached patch that fix regresion by. commit c7cef0a849
>> ("console: Add extensible console matching")
>>
>> or you have better way?
>
> Please re-read my first response to this problem.
>

> Also, this expectation is an impediment when adding support for other
> 8250-like designs that don't have the same 8250 divisor registers
> (ie., _every_ new design). To properly support this requirement for
> just the existing 8250 hardware will require special probe_baud()
> functions for: dw_8250, intel byt, intel mid, omap_8250, exar 17v35 series,
> omap 1510.

But you can not break old setup!

old behavior: console=uart8250,io,0x3f8

when bootloader or firmware has 115200 used already,
earlycon, and console all keep 115200.

Now with your change, earlycon will use 115200 still,
but console will switch to 9600.

>
> Is specifying the line speed on the command line really a burden?
>

Yes.  We have two setups, and two BIOS versions.
product version is using 9600 and devel/debug is using 115200.

This is a regression, and must be addressed.

Greg,

Please don't send merge request for tty-next to Linus before
this regression get resolved.

Thanks

Yinghai
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