linux-kernel - Re: [PATCH v1 3/4] max3100: adds console support for MAX3100

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Date:	Mon, 29 Mar 2010 08:11:15 +0200
From:	christian pellegrin <chripell@...e.org>
To:	Feng Tang <feng.tang@...el.com>
Cc:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"greg@...ah.com" <greg@...ah.com>,
	"david-b@...bell.net" <david-b@...bell.net>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>,
	"spi-devel-general@...ts.sourceforge.net" 
	<spi-devel-general@...ts.sourceforge.net>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 3/4] max3100: adds console support for MAX3100

On Mon, Mar 29, 2010 at 4:48 AM, Feng Tang <feng.tang@...el.com> wrote:
> Hi,

Hi,

>
> I modified the code a little and run it on our HW platform, it really show
> some sigh of life: it can boots to console (the print format is not so good),
> I can input command and it execute correctly, but very slow, I type 3
> characters and it takes about 2 seconds to echo back on screen and start the
> execution, and after about 1 minute, the console hang there and input stopped
> to work.

never seen such a behavior. Which platform are you using? Which SPI
driver? Do you have a low level printk (printascii) that puts output
somewhere else so I can send you a patch with some debugging output?
Can you log in some other way (like via network) and see if the CPU
load is at 100% for some reason?

>> This patch adds console support for the MAX3100 UART
>> (console=ttyMAX0,11500). The SPI subsystem and an
>
> 115200?
>

ack

> Does this imply to have to work with HW flow control? on my platform
> I have to remove the RTS bit to make it work.
>

no, I put RTS on  because it looks like a good default. I can make it
configurable. I just noticed on the data sheet that RTS is actually
inverted so a more sensible default would be to put it off. For
testing you should have flow control set to none on the machine you
are using as a terminal emulator.

>> +             max3100_sr(s, tx, &rx);
>
> It doesn't handle received characters here? If the console is printing out
> a bulk of message while user input some command, the command may be ignored.
> Myself have met the same problem in our driver.
>

yes but I think it's quite difficult to solve this problem in every
case. Console output is massively used only on boot when the user is
not supposed to type a lot.

>> +     if (next != s->console_tail) {
>> +             s->console_buf[next] = ch;
>> +             s->console_head = next;
>> +     }
>
> Also I saw max3100_sr() uses cpu_to_be16() and be16_to_cpu(), is it really
> necessary, our platform is little-endian(x86), and I have to disable them
> to make the code work. Is your test platform big-endian?
>

Have you configured your SPI controller as LSB first somehow, haven't
you? BTW my platform is a quite usual ARM9 S3C2440 which is little
endian.


-- 
Christian Pellegrin, see http://www.evolware.org/chri/
"Real Programmers don't play tennis, or any other sport which requires
you to change clothes. Mountain climbing is OK, and Real Programmers
wear their climbing boots to work in case a mountain should suddenly
spring up in the middle of the computer room."
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