[driverloader] Re: [LinuxR3000] Broadcom 54g + FC3 + 1.5 G = 100% CPU usage?

[Prarit Bhargava]

Gus and Jonathan (at Linuxant support),

Linuxant does suffer from this problem.   The issue is NOT in Linux or 
in the wrapper SW, but is in the Broadcom driver/hardware (I can't be 
sure which) .  Either the driver or the hardware is restricted to < 1G 
support.

IMO the only way to determine whether the driver or the hardware is the 
problem, and move forward with any investigation is to get out a PCI bus 
analyzer (not likely :) ) or to find a Broadcom HW Spec.  I've been 
looking for the spec but haven't found one ...

There are other options (as I indicated below in my email this 
morning).  However, after thinking about that solution I realize that 
forcing DMA under 1 G is a signifigant performance hit... which pretty 
much eradicates the whole point of 54g.

I suppose that the wrapper could enforce the restriction but I'm 
obviously unsure of how that code is archetected ...

P.

Constantine 'Gus' Fantanas wrote:

> What about the Linuxant driver?  Does it suffer from the same bug?
>
> Gus Fantanas
>
>
> On Monday 28 March 2005 07:54 am, Prarit Bhargava wrote:
>  
> Hi everyone,
>
> Larry wrote:
>
> >Another interesting side note:  After testing with a single 1GB stick, I
> >found ndiswrapper worked properly, then I bumped it back up to 2GB.  
> With
> >the 2GB back in place, I decided to test ndiswrapper again, and 
> amazingly
> >it worked perfectly.  I rebooted again, and it stopped working.  Weird.
>
> Please read on -- I know why this works/doesn't work ;)
>
> A little kernel hacking, and I discovered the following:
>
> Anytime the Broadcom hardware makes a DMA transaction ABOVE the 1 G
> boundary I end up with the system hang we're all experiencing.*  The
> driver appears to initialize properly, setup up PCI IO/MEM allocs, etc.,
> without any issues.  It's only when the driver
> starts negotiating do I run into a problem.  The driver negotiation, as
> with many PCI requests, requires a DMA transaction.
>
> Obviously, I don't have access to the Broadcom Windoze sources otherwise
> hackery would have already ensued :) .. and this list would be in
> possession of a functional driver :)
>
> The 1 G boundary means one of two things:
>
> 1.  The driver is built around a 1 G DMA limit.  ... .... but why would
> Broadcom ever do such a thing?
>
> 2.  The hardware is built around a 1 G address limit ... .... but why
> would Broadcom ever release a brain-dead device like that?  And more
> importantly, why would HP/Compaq sell it?  IMO, if it is the hardware,
> I'm going to be returning my laptop.
>
> Back to the case Larry raises above where the card seems to work and
> then after a reboot it doesn't.  It seems to depend on whether or not
> you're DMAing to a physical memory address above the 1 G boundary.  If
> you do -- you're going to hang.  If you don't (ie, you get lucky) you
> should be alright.
>
> Hope this helps,
>
> P.
>
> * I did come up with an obvious work around -- add "mem=1024M" to the
> boot command line (grub, lilo... whatever you're using).   Of course,
> this does limit your memory to 1 G.  Also, if I have the time this week
> I may hack the FC3 kernel to handle DMA from the Wireless such that it
> only DMAs to addresses below 1 G.  Yes, this is a very ugly brute-force
> attempt to get it working ... no promises that it will be this week
> though ...