Hi Bjørn,
Thank you for your answer.
19.06.2010 18:34, Bjørn Mork kirjoitti:
[ I think this should have been posted to linux-media@xxxxxxxxxxxxxxx instead ]
Marko Ristola<marko.ristola@xxxxxxxxxxx> writes:
I am now subscribed into that list too, but maybe I start with the
small patches instead of the big patch.
Hello all interested in a robust Mantis driver.
I have done some Mantis DMA fixes about two to four years ago
into v4l-dvb/linux/drivers/dvb/media/mantis/mantis_dma.c,
but they were discarded then, but the problems remained.
Those fixes helped at least one individual with Cinergy C PCI HD card
too by lessening the number
of artifacts and making the card usable. I sent the patches for many
Finnish people at those years.
I find this very interesting. I have two DVB-C cards, where one of them
is a Terratec Cinergy C, and I do see the occasional stuck CPUs. Never
realized that the mantis driver might be the cause of that.
I can't see the spin lock bug because I have now only one CPU.
tasklet disable/enable is an easy thing to start bug exclusion.
For Mauro and other maintainers - the patch in this email is now
against current Mercurial http://linuxtv.org/hg/v4l-dvb branch.
What do you think about this patch? Could you apply it?
I accept that this code may be added to Linux Kernel, or somewhere
else, licensed as GPLv2.
This code is fully written by me (Marko Ristola).
Signed-off-by: Marko Ristola<marko.ristola@xxxxxxxxxxx>
I am not Mauro (or other maintainers :-), but I guess you will have a
much better chance getting this properly reviewed if you move to git,
split up the patch according to your very good 4 point description, and
use that description as a commit message for the patches.
This will also allow the rest of us to test the effect of each issue
independently.
Probably Mauro doesn't even be on the old list any more.
The patch does two things (other two things are just thoughts, related
to robustness):
1. Don't flush 64K garbage at stream start, occurs if mantis_dma_start
is run more than once.
This fix could be done with altering only about two lines of code by
fixing the broken DMA RISC program code.
(Bug description: At line[0] RISC IRQ will store line=15 on current
code, causing copying of lines between 0 and 14, and next time 15 from
previous DVB TS stream (total 64K garbage). After that line=0 contains
current stream, no garbage.
Bug fix description: RISC program must store at interrupt the active
line variable's value, instead of ( (line - 1) mod 16)).
This sounds like a real bug. Maybe a candidate for stable as well?
Yes, this is a bug and it is easy to fix.
On my patch, it seems, that risc_step=0 point could be used for the
interrupt instead of risc_step=1, thus making the code a bit easier to
understand.
2. Alter DMA transfer so, that each DMA transfer copies only complete
packets (either 188 or 204 bytes) with each DMA transfer.
The hypothesis is that if a DMA transfer transfers only a part of the
188/204 sized packet,
that packet gets corrupted (last bytes of 2048 sized block).
My DMA transfers are aligned by 64 bytes in CPU memory (DMA buffer
start + multiple of 16x(188 or 204)).
I cannot really understand how such corruption could happen, unless
there are other bugs here? And if there are, then anything hiding them
would be bad...
Mantis PCI card receives by radio 188/204 byte sized packets.
If there are CRC errors with those, they are counted by the PCI card.
If there are zero fatal CRC errors counted, but even then some packets
are missing from a recording,
there is a serious problem between the radio and the disk storage.
The DMA transfer from PCI to CPU DMA buffer and the copying from CPU DMA
buffer to generic v4l-dvb code
are the only Mantis specific tasks. All other is used so much, that they
should be seen by everyone.
I'll try to proof it. If I can't prove it, no code is needed to fix it.
3. tasklet_enable/ tasklet_disable for DMA start/stop is commented out
on my patch.
I think that tasklet enabling maintenance should be done at these
points, but I don't know
whether the lack of those might cause spin lock failures. Lack of
these might
cause problems while switching channels (EPG search switches frequency).
Sounds reasonable. Did you try it?
I didn't have time yet, thus I commented it out.
4. There is some problem with rmmod mantis, do lsmod:
Module Size Used by
tda10021 5486 4294967291
modprobe mantis
tda10021 5486 4294967292 mantis
So the reference count from mantis to tda10021 gets corrupted at rmmod.
I have Fedora 13 kernel, 2.6.33.5-124.fc13.x86_64
FWIW, I do not see this running a Debian kernel (2.6.32-5-amd64) with a
backported mantis driver (from 2.6.35-rc1).
Module Size Used by
tda10021 4774 1 mantis
# rmmod mantis
tda10021 4774 0
# modprobe mantis
tda10021 4774 1 mantis
Good that it works for you. The bug I see is a minor thing, because the
computer doesn't crash.
The second modification is the reason for the big number of changes.
This is also the patch, that isn't easily acceptable, because it is hard
to proof that the packets do get corrupted at DMA transfer cutting
points, or that the hard lockups/reboots are caused
by the DMA transfer misalignment by 188/204 bytes.
The reasoning for the fix is, that without this alignment change there
were too many artefacts (VDR DVB
recordings lost sound after a while, thus VDR recording feature was
unusable).
This sounds a bit like magic to me. Any idea why such a change would
make any difference?
I have to try to prove that the problem exists without my modifications.
But with these modifications on recordings the sound was
usable. Picture artefacts weren't so fatal at real time, even
though on Windows side there were much less picture artefacts.
I haven't really thought much about artefacts, but I do notice a sharp
high pitched sound now and then. Might be a symptom?
Maybe not. If you see no CRC warnings about lost packets (tzap or
something), and
the recording done does have lost packets, I think that the problem has
been proved.
Of course, the initial 64K data have to be excluded first.
For historical reasons, I need still to modprobe mantis by hand,
and then the drivers get probed and loaded. Usually PCI device drivers
get loaded automatically.
You are aware of the patch at
http://jusst.de/hg/mantis-v4l-dvb/rev/3731f71ed6bf
?
Seems interesting. I need to look at these tables. Maybe the modprobe
problem I saw is caused by missing table entries in my case.
Maybe I will get the remote control work again some day.
I need a better picture first though.
Bjørn
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Best Regards,
Marko Ristola
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