[parisc-linux] serial baud_base, high baud rates and divisors

[parisc-linux] serial baud_base, high baud rates and divisors

[Enrik Berkhan]

Hi,

when using a 720 (running linux, of course ;-) as serial console
for a 715(old) I've noticed that the terminal (720) produces garbage
when the 715 comes to the firmware prompt (both running at 115200).
This is not a flow control or something problem. Investigating on
that I've found some oddities concerning setserial, baud_base and
the divisor calculation in the serial driver ...

- by default all parisc serial devices' baud_base is set to 454545
  (derived from the LASI UART crystal's frequency). The actual divisor
  is calculated in change_speed() of serial.c to be

  quot = baud_base / baud;

  with all integers. Thus, 454545 / 115200 = 3. The resulting baud
  rate should be something like 454545 / 3 = 151515. That's somewhat
  far away from 115200, explaining the garbage.

- I've made a simple measurement of the actual baud rate using a DMM
  with builtin frequency counter: set the port to 8N1 and outputting
  0x55 continously should produce a square wave of half the baud rate
  frequency at the transmit pin. So I've verified that at least the
  720 seems to have a real baud_base of 460800 (the measured frequency
  was 57.6kHz for a divisor of 4).

- trying to change the baud_base using setserial to 460800 failed with
  EADDRINUSE. I've found the reason to be a loop in set_serial_info():

        /* Make sure address is not already in use */
        if (new_serial.type) {
                for (i = 0 ; i < NR_PORTS; i++)
                        if ((state != &rs_table[i]) &&
                            (rs_table[i].port == new_port) &&
                            rs_table[i].type)
                                return -EADDRINUSE;
        }

  Memory mapped parisc ports all have port == 0, so this has to fail.
  Temporary workaround: `setserial /dev/ttyS1 port 0x10000 ...' once
  will prevent the above loop from finding conflicts.

So, the following things have to be fixed:

- get/set_serial_info have to be enhanced for memory mapped ports
- setserial should be enhanced accordingly
- divisor calculation should be changed at least to round to nearest,
  not round towards zero, or LASI ports might still suffer from the first
  problem _if_ they really have baud_base 454545
- baud_base should be initialized correctly for other gsc based ports.

If someone can confirm my analysis and tell me the direction of how to
fix these things I would be willing to work on it (shouldn't be hard,
maybe boring ;-).

Enrik
-- 
Enrik Berkhan                                         plan b. GmbH
                                                      Rüppurrer Straße 4
+49-721-388582 (voice)                                76137 Karlsruhe
+49-721-388581 (fax)                                  Germany

Re: [parisc-linux] serial baud_base, high baud rates and divisors

[Helge Deller]

On Thursday 07 February 2002 13:08, Enrik Berkhan wrote:
> Hi,
>
> when using a 720 (running linux, of course ;-) as serial console
> for a 715(old) I've noticed that the terminal (720) produces garbage
> when the 715 comes to the firmware prompt (both running at 115200).
> This is not a flow control or something problem. Investigating on
> that I've found some oddities concerning setserial, baud_base and
> the divisor calculation in the serial driver ...

AFAIK the firmware output only happens at 9600 baud (8N1) and you can't 
change that. After the linux kernel has booted you can of course use
a higher rate.

Helge
-- 
Helge Deller
SAP AG - LinuxLab and Unix Platforms
email: helge.deller@sap.com

Re: [parisc-linux] serial baud_base, high baud rates and divisors

[Enrik Berkhan]

On Thu, Feb 07, 2002 at 03:41:34PM +0100, Helge Deller wrote:
> AFAIK the firmware output only happens at 9600 baud (8N1) and you can't 
> change that. After the linux kernel has booted you can of course use
> a higher rate.

The firmware allows higher baud rates, at least on the 710, 715 and 720.
I'm using it, so it does work ;-) Try "help rs232" when in boot admin
mode.


Enrik
-- 
Enrik Berkhan                                         plan b. GmbH
                                                      Rüppurrer Straße 4
+49-721-388582 (voice)                                76137 Karlsruhe
+49-721-388581 (fax)                                  Germany

Re: [parisc-linux] serial baud_base, high baud rates and divisors

[Grant Grundler]

Helge Deller wrote:
> AFAIK the firmware output only happens at 9600 baud (8N1) and you can't 
> change that.

Actually, I think one can. But I doubt HP is going to fix any firmware
bugs related to console speeds other than 9600.

Running 19200 was crashing A500 console/GSP last year. I finally
convinced the firmware team it was the same problem that happened
at 9600 (less frequently of course).
I haven't verfied it was fixed in new PDC.

grant

Re: [parisc-linux] serial baud_base, high baud rates and divisors

[Grant Grundler]

Enrik Berkhan wrote:
> Investigating on
> that I've found some oddities concerning setserial, baud_base and
> the divisor calculation in the serial driver ...

good work.

...
>   Memory mapped parisc ports all have port == 0, so this has to fail.
>   Temporary workaround: `setserial /dev/ttyS1 port 0x10000 ...' once
>   will prevent the above loop from finding conflicts.
> 
> So, the following things have to be fixed:
> 
> - get/set_serial_info have to be enhanced for memory mapped ports
> - setserial should be enhanced accordingly

If other non-intel architectures don't have a solution for this.
My first thought was to assign fake port addresses.

Do PCI serial cards also use MMIO?

> - divisor calculation should be changed at least to round to nearest,
>   not round towards zero, or LASI ports might still suffer from the first
>   problem _if_ they really have baud_base 454545
> - baud_base should be initialized correctly for other gsc based ports.

We'd have to dig a bit for documentation on this.
Please poke me offline if that doesn't happen in the next week or so.

> If someone can confirm my analysis and tell me the direction of how to
> fix these things I would be willing to work on it (shouldn't be hard,
> maybe boring ;-).

cool - thanks,

grant

Re: [parisc-linux] serial baud_base, high baud rates and divisors

[Enrik Berkhan]

On Thu, Feb 07, 2002 at 09:31:07AM -0700, Grant Grundler wrote:
> > - get/set_serial_info have to be enhanced for memory mapped ports
> > - setserial should be enhanced accordingly
> 
> If other non-intel architectures don't have a solution for this.
> My first thought was to assign fake port addresses.

Looks like most other architectures have their own code even when
using 16450 like UARTs (e.g. arch/mips/au1000/common/serial.c).
Especially set_serial_info is architecture dependent, because it just
doesn't make much sense to fiddle with irq and port settings on
parisc, does it? Faking port adresses could be a workaround, but it's
not clean as it might make the ports show up in /proc/ioports ...

But enhancing the test for doubly assigned ports to

      if ((rs_table[i].port == port) &&
          (rs_table[i].iomem_base == req->iomem_base))

might be ok. This code can be found in register_serial().

BTW, drivers/gsc/serial.c does no request_mem_region(). Is this in-
tentional?

> Do PCI serial cards also use MMIO?

I don't know.

> > - baud_base should be initialized correctly for other gsc based ports.
> 
> We'd have to dig a bit for documentation on this.
> Please poke me offline if that doesn't happen in the next week or so.

The hardball ers states a 7.3728MHz (== 16 * 460800) baud rate clock,
which confirms the output of my DMM. So we would need a table holding
the baud_base for each device?

Enrik
-- 
Enrik Berkhan                                         plan b. GmbH
                                                      Rüppurrer Straße 4
+49-721-388582 (voice)                                76137 Karlsruhe
+49-721-388581 (fax)                                  Germany

Re: [parisc-linux] serial baud_base, high baud rates and divisors

[Grant Grundler]

Enrik Berkhan wrote:
> But enhancing the test for doubly assigned ports to
> 
>       if ((rs_table[i].port == port) &&
>           (rs_table[i].iomem_base == req->iomem_base))
> 
> might be ok. This code can be found in register_serial().

Yeah - you are right.

> BTW, drivers/gsc/serial.c does no request_mem_region(). Is this in-
> tentional?

probably. Check if an entry for serial exists in /prc/iomem.
At one point, the device discover code was changed to automatically
do the request_mem_region() devics firmware told us about.

> The hardball ers states a 7.3728MHz (== 16 * 460800) baud rate clock,
> which confirms the output of my DMM. So we would need a table holding
> the baud_base for each device?

Dunno. We might given different generations of HW.

grant

Re: [parisc-linux] serial baud_base, high baud rates and divisors

[Matthew Wilcox]

On Sat, Feb 09, 2002 at 11:50:20PM -0700, Grant Grundler wrote:
> Enrik Berkhan wrote:
> > BTW, drivers/gsc/serial.c does no request_mem_region(). Is this in-
> > tentional?
> 
> probably. Check if an entry for serial exists in /prc/iomem.
> At one point, the device discover code was changed to automatically
> do the request_mem_region() devics firmware told us about.

Where `one point' == `last night' :-)

I'm not quite sure about the way I've done it -- I might set it up to
always claim rather than only claim on device detection, and take the
name from the hardware database rather than the driver.

I suspect I've broken module unload with the current code, and I need
a release_mem_region on deregistration... investigating now.

-- 
Revolutions do not require corporate support.