Problem of concurrency in arch/ppc/8260_io/uart.c

[Steffen Rumler]

Hi,

I have seen a similar problem for the 2.4.20.

When I force a lot of console output via the following command:

   while true; do cd /; ls -R; done

and type-in some letters in parallel, the console
becomes crazy.

I have added some instrumentation in order to dump the
TX Buffer Descriptor Table. I have found that the
hardware pointer (TBPTR) and the software pointer (tx_cur)
are not more synchronized together:

 >> make new rlogin session <<
/root# cd /proc/driver

/root# cat uart-bdtables; cat mpc82xx/smc1_pram | grep SMC1_PRAM_TBPTR

TX BD table
   (000 at 0xfff005f0) status: 0x1000 len: 0001 addr: 0x001bb084
   (001 at 0xfff005f8) status: 0x1000 len: 0001 addr: 0x001bb0a4
* (002 at 0xfff00600) status: 0x1000 len: 0001 addr: 0x001bb0c4
   (003 at 0xfff00608) status: 0x3000 len: 0004 addr: 0x001bb0e4
    SMC1_PRAM_TBPTR            0x20         2     0600

    --> hardware and software pointer still synchronized

    >> force console to become crazy (see above) <<

/root# cat uart-bdtables; cat mpc82xx/smc1_pram | grep SMC1_PRAM_TBPTR

TX BD table (tbptr: 0x00000088)
   (000 at 0xfff005f0) status: 0x1000 len: 0003 addr: 0x001bb084
* (001 at 0xfff005f8) status: 0x1000 len: 0021 addr: 0x001bb0a4
   (002 at 0xfff00600) status: 0x1000 len: 0001 addr: 0x001bb0c4
   (003 at 0xfff00608) status: 0x3000 len: 0001 addr: 0x001bb0e4
    SMC1_PRAM_TBPTR            0x20         2     0600

    --> hardware and software pointer NOT more synchronized

    >> make additional console output: echo foo >/dev/console <<

/root# cat uart-bdtables; cat mpc82xx/smc1_pram | grep SMC1_PRAM_TBPTR

* (000 at 0xfff005f0) status: 0x1000 len: 0003 addr: 0x001bb084
   (001 at 0xfff005f8) status: 0x9000 len: 0004 addr: 0x001bb0a4
   (002 at 0xfff00600) status: 0x1000 len: 0001 addr: 0x001bb0c4
   (003 at 0xfff00608) status: 0x3000 len: 0001 addr: 0x001bb0e4
    SMC1_PRAM_TBPTR            0x20         2     05f0

    --> hardware pointer hangs at 0x5f0 because R-Bit not set, but
        at 0x5f8

Inside uart.c, there are the following output routines:

   rs_8xx_put_char()
   rs_8xx_write()
   rs_8xx_send_xchar()
   my_console_write()

I think there must be a synchronization accessing the
TX BD table. I suggest the patch attached.


Best Regards
Steffen
--


--------------------------------------------------------------

Steffen Rumler
ICN CP D NT SW 7
Siemens AG
Hofmannstr. 51                 Email: Steffen.Rumler at siemens.com
D-81359 Munich                 Phone: +49 89 722-44061
Germany                        Fax  : +49 89 722-36703

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