[linux-dvb] Re: Too much memory???

[Michael Hunold <hunold@convergence.de>]

Hello Laurence,

> I've recently started testing 2.5.7x kernels and dvb-kernel with a
> NOVA-T PCI in the UK.
Thanks for testing and reporting the bugs!


> _______________________________________
> Jul 12 17:41:53 holmes kernel: saa7146: register extension 'budget dvb'.
> Jul 12 17:41:53 holmes kernel: saa7146: found saa7146 @ mem f8c37000
> (revision 1, irq 17) (0x13c2,0x1005).
> Jul 12 17:41:53 holmes kernel: DVB: registering new adapter
> (TT-Budget/WinTV-NOVA-T  PCI).
> Jul 12 17:41:53 holmes kernel: ------------[ cut here ]------------
> Jul 12 17:41:53 holmes kernel: kernel BUG at
> drivers/media/common/saa7146_core.c:67!
> Jul 12 17:41:53 holmes kernel: invalid operand: 0000 [#1]
> Jul 12 17:41:53 holmes kernel: CPU:    0
> Jul 12 17:41:53 holmes kernel: EIP:

Please run the bug through the tools "ksymoops", ie. do a "dmesg | 
ksymopps" and post the resulting file. This will decode the numbers to 
usable functions names and the like.

> I've spent a load of time building and rebuilding kernels because one
> moment the "budget" module would load and the next it would seg-fault on
> insertion with a BUG error in saa7164_core.c:67.
> After two successful runs with 2.5.73 and the CVS of the day (early
> July), everything just stopped working.  Everytime I load the modules I
> get the error described.
> Further investigation suggested that this may be due to the amount of
> memory I have installed on this box (recently increased to 1.2GB).
>
> If I specify `mem="900M"' when booting - limiting the available memory
> to less than 1GB - I can install the dvb modules.
Please have a look at the file "saa7146_core.c". There it says:
----------------------schnipp-------------------------------------
/* this is videobuf_vmalloc_to_sg() from video-buf.c */
static struct scatterlist* vmalloc_to_sg(unsigned char *virt, int nr_pages)
{
[...]
		if (PageHighMem(pg))
			BUG();
----------------------schnipp-------------------------------------

The driver needs to build so-called scatter/gather lists for the memory 
where the hardware will write it's data to, that means a description of 
the memory locations. If you have more than 1 GB of memory, you need 
something called "high-memory support" within Linux. If you do this, 
it's possible that the memory allocated by the driver will be above > 1 
GB, and the function will fail with a call to BUG().

In theory, the hardware can do a DMA up to 4 GB, but I don't know if 
there is something with the memory management of Linux that prevents this.

> If I don't - this is what I get....can anyone help?
It's mentioned in the code that the functions was basically taken from 
"video-buf.c" from Gerd Knorr. Perhaps he can bring some light into this 
issues. I've send him a CC of this mail.

For the meantime, you need to disable high memory support or limit the 
amount of memory.

> Laurence
CU
Michael.



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