Cinergy T2 stopped working with kernel 2.6.30

Cinergy T2 stopped working with kernel 2.6.30

[emagick]

My Cinergy T2 (T²) doesn't work with kernels 2.6.30, 2.6.30.1, and 2.6.31-rc3,
but it works with kernel 2.6.29. The kernel logs

    dvb-usb: recv bulk message failed: -110

and the application (I've tried mythtv and mplayer) trying to access the DVB receiver
times out when trying to tune to a channel.

Is there anyone for whom dvb_usb_cinergyT2 of kernel 2.6.30 or later does work?

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

There are two new discoveries about my Cinergy T2 problem:

- the Cinergy T2 works when attached to an Intel Core2 board, but doesn't work when
   attached to an Intel Atom N270 board (tuning times out)

- "git bisect" of the Linux kernel points to a bad merge of
   commit 60db56422043aaa455ac7f858ce23c273220f9d9 (good) and
   commit be0ea69674ed95e1e98cb3687a241badc756d228 (good) yielding
   commit 6e15cf04860074ad032e88c306bea656bbdd0f22 (bad).

So, the problem is probably interrupt-related, not dvb-usb-related.
Any idea on how to continue from here?

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

The more I look into this problem the stranger it becomes. I've compiled
the kernel for different CPUs:

                  |    mplayer               mythtv
-----------------+--------------------------------------------
CONFIG_M486      |    works                 works
CONFIG_M586      |    works                 cannot tune
CONFIG_MCORE2    |    cannot tune           cannot tune

These results are for my Atom N270 board. On my Core2 board, the Cinergy T2 works
all the time.

By applying -march=i486 and -march=i586 to individual source files, I found
out that dvb_frontend.c is the culprit.

By editing the assembly output for dvb_frontend.c, I found out that only
dvb_frontend_swzigzag_autotune() needs to be compiled with CONFIG_M486 to
make the Cinergy T2 work, everything else can be compiled with CONFIG_M586.

Both compiled versions of dvb_frontend_swzigzag_autotune() look OK (but I
haven't yet strictly verified the assembly code). Anyway, nothing in that
code should make a difference on N270 vs. Core, except for timing. Adding
NOPs doesn't seem to make a difference.

Any ideas? Could this be a CPU bug?

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

I've now compared the generated assembly code for dvb_frontend_swzigzag_autotune()
built with CONFIG_M486 vs. CONFIG_M586. Both versions are correct, but the one compiled
with -march=i586 (for which tuning does not work) uses more stack space (one 32-bit
word).

Does this ring any bells?

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

I've added dummy 32-bit variables to dvb_frontend_swzigzag_autotune() to change the
frame size. Here are the results for mythweb (can tune/cannot tune):

#variables     i486       i586
  0             ok         failure
  1             failure    ok
  2             ok         ok
  3             failure    failure
  4             failure    ok
  5             ok         ok
  6             ok         ok
  7             ok         ok
  8             ok         failure
  9             failure    ok
10             ok         ok
11             ok         failure
12             failure    ok
13             ok         ok
14             ok         ok
15             ok         ok
16             ok         ok
17             ok         ok
18             ok         failure
19             ok         failure
20             failure    ok

There's a pattern with some exceptions. Could be an alignment-related problem.

Anyone listening?

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

Addendum: with 3 additional local variables and compiled for i486 mythweb fails to
tune, but mplayer can tune. Note that I mentioned cases where mplayer can tune but
mythweb fails to tune. Perhaps alignment in the user-mode stack is a factor.

Anyone listening?

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

I wrote:

> Addendum: with 3 additional local variables and compiled for i486 mythweb fails to
> tune, but mplayer can tune. Note that I mentioned cases where mplayer can tune but
> mythweb fails to tune. Perhaps alignment in the user-mode stack is a factor.

Oops, there was no instance of mythweb being able to tune, but mplayer not
being able to tune. Sorry.

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

I think I've found the problem:

------------------------------------------------------------------------
static int cinergyt2_fe_set_frontend(struct dvb_frontend *fe,
				  struct dvb_frontend_parameters *fep)
{
	struct cinergyt2_fe_state *state = fe->demodulator_priv;
	struct dvbt_set_parameters_msg param;
	char result[2];
	int err;

	param.cmd = CINERGYT2_EP1_SET_TUNER_PARAMETERS;
	param.tps = cpu_to_le16(compute_tps(fep));
	param.freq = cpu_to_le32(fep->frequency / 1000);
	param.bandwidth = 8 - fep->u.ofdm.bandwidth - BANDWIDTH_8_MHZ;

	err = dvb_usb_generic_rw(state->d,
			(char *)&param, sizeof(param),
			result, sizeof(result), 0);
------------------------------------------------------------------------

As dvbt_set_parameters_msg is declared with __attribute__((packed)), its
alignment is 8 bits.  In fact, cinergyt2_fe_set_frontend()'s param variable
is not aligned on a 32-bit boundary. Note that param is passed to usb_bulk_msg().
This seems to cause DMA problems on my hardware (Atom N270 + 945GSE + ICH7M).

I hope that I'm not talking to a black hole.

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

Unfortunately, aligning cinergyt2_fe_set_frontend()'s param and result on a 32-bit
boundary doesn't help.

Re: Cinergy T2 stopped working with kernel 2.6.30

[emagick]

Apparently, usb_bulk_msg() cannot be used with data on the stack:

http://www.linuxtv.org/pipermail/linux-dvb/2008-August/028150.html
http://www.mail-archive.com/linux-usb-devel@lists.sourceforge.net/msg19158.html

Re: Cinergy T2 stopped working with kernel 2.6.30

[Markus Rechberger]

On Fri, Jul 31, 2009 at 9:47 PM, <emagick@magic.ms> wrote:
> Apparently, usb_bulk_msg() cannot be used with data on the stack:
>
> http://www.linuxtv.org/pipermail/linux-dvb/2008-August/028150.html
> http://www.mail-archive.com/linux-usb-devel@lists.sourceforge.net/msg19158.html
> --

As far as I recall this has been documented for ages already...
Although many people stumble over it... last but not least there's no reason to
have USB drivers in the kernel anyway..

Markus

Re: Cinergy T2 stopped working with kernel 2.6.30

[Johannes Stezenbach]

On Fri, Jul 31, 2009 at 08:44:59PM +0200, emagick@magic.ms wrote:
> ------------------------------------------------------------------------
> static int cinergyt2_fe_set_frontend(struct dvb_frontend *fe,
> 				  struct dvb_frontend_parameters *fep)
> {
> 	struct cinergyt2_fe_state *state = fe->demodulator_priv;
> 	struct dvbt_set_parameters_msg param;
> 	char result[2];
> 	int err;
> 
> 	param.cmd = CINERGYT2_EP1_SET_TUNER_PARAMETERS;
> 	param.tps = cpu_to_le16(compute_tps(fep));
> 	param.freq = cpu_to_le32(fep->frequency / 1000);
> 	param.bandwidth = 8 - fep->u.ofdm.bandwidth - BANDWIDTH_8_MHZ;
> 
> 	err = dvb_usb_generic_rw(state->d,
> 			(char *)&param, sizeof(param),
> 			result, sizeof(result), 0);
> ------------------------------------------------------------------------
> 
> As dvbt_set_parameters_msg is declared with __attribute__((packed)), its
> alignment is 8 bits.  In fact, cinergyt2_fe_set_frontend()'s param variable
> is not aligned on a 32-bit boundary. Note that param is passed to usb_bulk_msg().
> This seems to cause DMA problems on my hardware (Atom N270 + 945GSE + ICH7M).

I doubt that.  AFAIK EHCI has no alignment requirements on data, and the
x86 architecture has DMA consistent caches.  The code in question is
broken on ARM. MIPS etc. but it should work (and according to you has
worked up to 2.6.29) on x86.  (I'm not at all against fixing the
code for MIPS/ARM but I don't think that would fix the problem for you.)

[PATCH] dvb-usb: fix tuning with Cinergy T2

[emagick]

Initialize param.flags.

Signed-off-by: Eberhard Mattes <eberhard.mattes@web.de>
---
Not setting param.flags was the real cause of the inability of the Cinergy T2
driver to tune under certain circumstances. Moving stuff from the stack to the
heap did not really solve the problem. As there are several other drivers which
pass buffers on the stack to the USB layer, I leave fixing that to others.
This patch is against 2.6.30.


--- a/drivers/media/dvb/dvb-usb/cinergyT2-fe.c	2009-06-10 05:05:27.000000000 +0200
+++ b/drivers/media/dvb/dvb-usb/cinergyT2-fe.c	2009-08-02 09:28:55.000000000 +0200
@@ -275,6 +275,7 @@ static int cinergyt2_fe_set_frontend(str
  	param.tps = cpu_to_le16(compute_tps(fep));
  	param.freq = cpu_to_le32(fep->frequency / 1000);
  	param.bandwidth = 8 - fep->u.ofdm.bandwidth - BANDWIDTH_8_MHZ;
+	param.flags = 0;

  	err = dvb_usb_generic_rw(state->d,
  			(char *)&param, sizeof(param),