Re: Kernel booting on serial console ... crawling

Re: Kernel booting on serial console ... crawling

[Robert Kaiser]

> I tried to boot my kernel using the serial console, using the
> console=ttyS0,115200 (it does the same thing with 9600) ... it work great
> until :
> 
> Freeing unused kernel memory: 36k freed
> serial console detected.  Disabling virtual terminals.
> console=/dev/ttyS0
> 
> At this point the output of the serial line slow down dramaticly ... almost
> to a halt ... I get 1 line every 30 seconds !!!
> 

Is this an AMD Elan's built-in serial port, perchance ?

Rob
 
----------------------------------------------------------------
Robert Kaiser                         email: rkaiser@sysgo.de
SYSGO RTS GmbH
Am Pfaffenstein 14                    phone: (49) 6136 9948-762
D-55270 Klein-Winternheim / Germany   fax:   (49) 6136 9948-10

Re: Kernel booting on serial console ... crawling

[Robert Schwebel]

Hi Rob,

On Fri, 9 Nov 2001, Robert Kaiser wrote:
> Is this an AMD Elan's built-in serial port, perchance ?

I got a patch for the Elan's serial port from Jason Sodergren some days
ago, but it's not clear to me what exactly the problem is with this port.
I'm using the serial console on a DIL/Net-PC without any problems so far.
Perhaps it might be a good idea to join forces and try to get a patch for
the Elan series into the main kernel?

However, my current affords can be found on

  http://www.schwebel.de/software/dnp/index_en.html

This currently implements a new CPU configuration parameter and a fix for
the clock on the Elan CPUs.

Robert
-- 
 +--------------------------------------------------------+
 |             Dipl.-Ing. Robert Schwebel                 |
 | Pengutronix - Linux Solutions for Science and Industry |
 |  Braunschweiger Straße 79, 31134 Hildesheim, Germany   |
 |     Phone: +49-5121-28619-0  Fax: +49-5121-28619-4     |
 +--------------------------------------------------------+

Re: Kernel booting on serial console ... crawling

[Robert Kaiser]

[-- Attachment #1: Type: text/plain, Size: 1508 bytes --]

Hi Robert,

Am Freitag,  9. November 2001 13:27 schrieben Sie:
> On Fri, 9 Nov 2001, Robert Kaiser wrote:
> > Is this an AMD Elan's built-in serial port, perchance ?
>
> I got a patch for the Elan's serial port from Jason Sodergren some days
> ago, but it's not clear to me what exactly the problem is with this port.
> I'm using the serial console on a DIL/Net-PC without any problems so far.
> Perhaps it might be a good idea to join forces and try to get a patch for
> the Elan series into the main kernel?
>
> However, my current affords can be found on
>
>   http://www.schwebel.de/software/dnp/index_en.html
>
> This currently implements a new CPU configuration parameter and a fix for
> the clock on the Elan CPUs.

This is interesting, I was not aware of the different clock frequency issue.

Anyway, the patch I am using to fix the crawling console output symptom on 
the Elan is entirely different (see attachment). It was originally posted by
Anders Larsen <a.larsen@identecsolutions.de> and we have been using
it with good success in our embedded Linux product for quite a while now.
The comments in the source describe the problem. Interestingly, even the
latest AMD Elan product (SC520) seems to have this problem too.

Rob

----------------------------------------------------------------
Robert Kaiser                         email: rkaiser@sysgo.de
SYSGO RTS GmbH
Am Pfaffenstein 14                    phone: (49) 6136 9948-762
D-55270 Klein-Winternheim / Germany   fax:   (49) 6136 9948-10

[-- Attachment #2: AMD Elan Workaround --]
[-- Type: text/x-c, Size: 3569 bytes --]

Index: sysgo/elinos/linux/drivers/char/serial.c
diff -c sysgo/elinos/linux/drivers/char/serial.c:1.2 sysgo/elinos/linux/drivers/char/serial.c:1.3
*** sysgo/elinos/linux/drivers/char/serial.c:1.2	Wed May 17 14:07:00 2000
--- sysgo/elinos/linux/drivers/char/serial.c	Wed Jun  7 15:19:53 2000
***************
*** 607,612 ****
--- 607,613 ----
  	int status;
  	struct async_struct * info;
  	int pass_counter = 0;
+ 	int iir;
  	struct async_struct *end_mark = 0;
  #ifdef CONFIG_SERIAL_MULTIPORT	
  	int first_multi = 0;
***************
*** 627,635 ****
  		first_multi = inb(multi->port_monitor);
  #endif
  
  	do {
  		if (!info->tty ||
! 		    (serial_in(info, UART_IIR) & UART_IIR_NO_INT)) {
  			if (!end_mark)
  				end_mark = info;
  			goto next;
--- 628,637 ----
  		first_multi = inb(multi->port_monitor);
  #endif
  
+ 	iir = serial_in(info, UART_IIR);
  	do {
  		if (!info->tty ||
! 		    ((iir = serial_in(info, UART_IIR)) & UART_IIR_NO_INT)) {
  			if (!end_mark)
  				end_mark = info;
  			goto next;
***************
*** 645,650 ****
--- 647,663 ----
  		if (status & UART_LSR_DR)
  			receive_chars(info, &status);
  		check_modem_status(info);
+ #ifdef CONFIG_AMD_ELAN
+ 		/*
+ 		** There is a bug (misfeature?) in the UART on the AMD Elan
+ 		** SC4x0 and SC520 embedded processor series; the THRE bit of
+ 		** the line status register seems to be delayed one bit
+ 		** clock after the interrupt is generated, so kludge this
+ 		** if the IIR indicates a Transmit Holding Register Interrupt
+ 		*/
+ 		if ((iir & UART_IIR_ID) == UART_IIR_THRI)
+ 			status |= UART_LSR_THRE;
+ #endif
  		if (status & UART_LSR_THRE)
  			transmit_chars(info, 0);
  
***************
*** 679,685 ****
   */
  static void rs_interrupt_single(int irq, void *dev_id, struct pt_regs * regs)
  {
! 	int status;
  	int pass_counter = 0;
  	struct async_struct * info;
  #ifdef CONFIG_SERIAL_MULTIPORT	
--- 692,698 ----
   */
  static void rs_interrupt_single(int irq, void *dev_id, struct pt_regs * regs)
  {
! 	int status, iir;
  	int pass_counter = 0;
  	struct async_struct * info;
  #ifdef CONFIG_SERIAL_MULTIPORT	
***************
*** 701,706 ****
--- 714,720 ----
  		first_multi = inb(multi->port_monitor);
  #endif
  
+ 	iir = serial_in(info, UART_IIR);
  	do {
  		status = serial_inp(info, UART_LSR);
  #ifdef SERIAL_DEBUG_INTR
***************
*** 709,714 ****
--- 723,739 ----
  		if (status & UART_LSR_DR)
  			receive_chars(info, &status);
  		check_modem_status(info);
+ #ifdef CONFIG_AMD_ELAN
+ 		/*
+ 		** There is a bug (misfeature?) in the UART on the AMD Elan
+ 		** SC4x0 and SC520 embedded processor series; the THRE bit of
+ 		** the line status register seems to be delayed one bit
+ 		** clock after the interrupt is generated, so kludge this
+ 		** if the IIR indicates a Transmit Holding Register Interrupt
+ 		*/
+ 		if ((iir & UART_IIR_ID) == UART_IIR_THRI)
+ 			status |= UART_LSR_THRE;
+ #endif
  		if (status & UART_LSR_THRE)
  			transmit_chars(info, 0);
  		if (pass_counter++ > RS_ISR_PASS_LIMIT) {
***************
*** 717,723 ****
  #endif
  			break;
  		}
! 	} while (!(serial_in(info, UART_IIR) & UART_IIR_NO_INT));
  	info->last_active = jiffies;
  #ifdef CONFIG_SERIAL_MULTIPORT	
  	if (multi->port_monitor)
--- 742,748 ----
  #endif
  			break;
  		}
! 	} while (!((iir = serial_in(info, UART_IIR)) & UART_IIR_NO_INT));
  	info->last_active = jiffies;
  #ifdef CONFIG_SERIAL_MULTIPORT	
  	if (multi->port_monitor)

Kernel booting on serial console ... crawling

[Patrick Allaire]

I tried to boot my kernel using the serial console, using the
console=ttyS0,115200 (it does the same thing with 9600) ... it work great
until :

Freeing unused kernel memory: 36k freed
serial console detected.  Disabling virtual terminals.
console=/dev/ttyS0

At this point the output of the serial line slow down dramaticly ... almost
to a halt ... I get 1 line every 30 seconds !!!

why is this slow down occuring ? the part which is 100% kernel is going fast
and ok, but when it become console related ... it slows down ?

thak you

Patrick Allaire
mailto:pallaire@gameloft.com
If you can see it, but it's not there, it's virtual. 
If you can't see it, but it is there, it's hidden. 
It you can't see it and it isn't there, it's gone.

Re: Kernel booting on serial console ... crawling

[Bradley D. LaRonde]

I've seen something like that when my serial driver wasn't getting
interrupts.

Regards,
Brad

"Patrick Allaire" <pallaire@gameloft.com> said:
> I tried to boot my kernel using the serial console, using the
> console=ttyS0,115200 (it does the same thing with 9600) ... it work great
> until :
>
> Freeing unused kernel memory: 36k freed
> serial console detected.  Disabling virtual terminals.
> console=/dev/ttyS0
>
> At this point the output of the serial line slow down dramaticly ...
almost
> to a halt ... I get 1 line every 30 seconds !!!

Re: Kernel booting on serial console ... crawling

[José Luis Domingo López]

On Tuesday, 06 November 2001, at 16:52:18 -0500,
Patrick Allaire wrote:

> 
> I tried to boot my kernel using the serial console, using the
> console=ttyS0,115200 (it does the same thing with 9600) ... it work great
> until :
> [...]
> At this point the output of the serial line slow down dramaticly ... almost
> to a halt ... I get 1 line every 30 seconds !!!
> 
Same problem seems to have happened here with 2.4.14 twice, but booting
as usual (no serial console, just keyboard + monitor).

First time I didn't care much because booted with "mem=8m" to test
system behaviour with little memory, and just when qmail was being
started from the init scripts, the system seemed to halt (not even
ALT-SysRq worked, just printed the action requested to the screen). But
I was no patient enough, and ended up rebooting the machine the hard way.

Today I booted my machine again, and this time during fsck the problem
appeared again: this time was a bit more patient and after several
seconds the boot process continued. ALT-SysRq didn't work until the
system "unfroze". This temporary "halt" happened several times during
the boot sequence, each time lasting a variable amount of seconds.

It's been 2 hours since that happened, and the machine is working
nicely so far.

Kernel configuration is the same as it was on, among others, 2.4.10,
2.4.12 and 2.4.13, but this problem only have showed with 2.4.14.

-- 
José Luis Domingo López
Linux Registered User #189436     Debian Linux Woody (P166 64 MB RAM)
 
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