Re: Kernel booting on serial console ... crawling

[Robert Kaiser <rob@sysgo.de>]

[-- 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)