linux-kernel - Re: [PATCH] serial: DCC(JTAG) serial and console emulation support

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Message-ID: <AANLkTi=8Et=Z6zrzbZa3L0MO=cBjjh7L=XU2=PDEbzWW@mail.gmail.com>
Date:	Thu, 7 Oct 2010 15:48:54 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	Daniel Walker <dwalker@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org,
	"Hyok S. Choi" <hyok.choi@...sung.com>,
	Tony Lindgren <tony@...mide.com>,
	Jeff Ohlstein <johlstei@...cinc.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Ben Dooks <ben-linux@...ff.org>,
	Alan Cox <alan@...ux.intel.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Feng Tang <feng.tang@...el.com>,
	Tobias Klauser <tklauser@...tanz.ch>,
	Jason Wessel <jason.wessel@...driver.com>,
	Philippe Langlais <philippe.langlais@...ricsson.com>
Subject: Re: [PATCH] serial: DCC(JTAG) serial and console emulation support

On Thu, Oct 7, 2010 at 15:39, Daniel Walker wrote:
> On Thu, 2010-10-07 at 15:25 -0400, Mike Frysinger wrote:
>> On Thu, Oct 7, 2010 at 14:36, Daniel Walker wrote:
>> > Many of JTAG debuggers for ARM support DCC protocol over JTAG
>> > connection, which is very useful to debug hardwares which has no
>> > serial port. This patch adds DCC serial emulation and the console
>> > support. System timer based polling method is used for the
>> > emulation of serial input interrupt handling.
>>
>> why use serial_core at all ?  seems like you could just use the tty
>> layer directly.  i did that with drivers/char/bfin_jtag_comm.c.
>>
>> although, there's the suggestion in the air that my jtag driver could
>> be converted to the HVC framework to even further simplify things.
>> but no one thinks it should be serial_core :).
>
> It will actually create a serial port on ttyS* if you want it to.. It
> could be debatable if that's useful, but I didn't rip that out because
> Hyok had that in his original code (he thought it was useful) ..

i dont think hijacking the "ttyS" namespace is acceptable, even if
it's behind a Kconfig.  other people have tried in the past (myself
included) and been shot down.  sounds like a shim for crappy userspace
apps that blindly assume /dev/ttyS*.  is that really an issue anymore
though now that things like /dev/ttyUSB* are so common and people are
used to picking between multiple serial sources ?
-mike
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