Bug 9408

I am not sure that this is a regression, a driver error, a hardware error, or an error in the firmware. What I do know for certain is that the reversion that "fixes" the problem is not the cause - it merely masks the real problem.

DMA for this device is accomplished by creating a Descriptor Ring Address buffer that can be accessed by the firmware, and creating a number of descriptors to populate the ring. Each such descriptor consists of 2 control words and two 32-bit quantities that contain the address of the DMA buffer. This scheme is similar to that used in the 30- and 32-bit DMA used by bcm43xx and b43 for all previous cards.

When commit 44048d70 is included, the ring buffer is located at a physical address equal to 0x5877E000 (~1.48 GB - this machine has 1.5 GB RAM). It fails with an RX error code indicating a descriptor read error. I tried booting with mem=1024M and mem=512M options. The error persisted.

After reverting the above commit, the ring buffer was located at a physical address of 0x0279A000 (~41 MB), which worked.

* bugme-daemon@bugzilla.kernel.org <bugme-daemon@bugzilla.kernel.org> wrote:

> When commit 44048d70 is included, the ring buffer is located at a 
> physical address equal to 0x5877E000 (~1.48 GB - this machine has 1.5 
> GB RAM). It fails with an RX error code indicating a descriptor read 
> error. I tried booting with mem=1024M and mem=512M options. The error 
> persisted.
> 
> After reverting the above commit, the ring buffer was located at a 
> physical address of 0x0279A000 (~41 MB), which worked.

that's interesting. What happens if you try a stupid hack that uses 
GFP_DMA to allocate the ringbuffer to below 16 MB - does that result in 
a working driver too?

	Ingo

With your suggested hack, the ring buffer is located at 0xA08000 and the system works. The data buffers are still at high addresses (~1.5 GB) - only the descriptor ring is at the low address.

This looks more and more like a firmware error.

I'm removing this issue from the list of recent regressions.

Please let me know if this bug should be closed.

The problem is that the BCM card with 64-bit DMA requires the descriptor ring to be in low-order memory. We have not delineated the boundary between good/bad behavior; however memory locations as low as 48M work. It may be that 64 M is tha "magic" boundary. For these chips, these buffers are allocated with the GFP_DMA flag, as though this device were an ISA interface. This has worked to date.

The real problem is likely an error in the chip itself.