Re: [BISECTED REGRESSION] b43legacy broken on G4 PowerBook

[Larry Finger]

On 6/7/19 12:29 PM, Christoph Hellwig wrote:
> I don't think we should work around this in the driver, we need to fix
> it in the core.  I'm curious why my previous patch didn't work.  Can
> you throw in a few printks what failed?  I.e. did dma_direct_supported
> return false?  Did the actual allocation fail?

Routine dma_direct_supported() returns true.

The failure is in routine dma_set_mask() in the following if test:

        if (!dev->dma_mask || !dma_supported(dev, mask))
                return -EIO;

For b43legacy, dev->dma_mask is 0xc265684800000000.
    dma_supported(dev, mask) is 0xc08b000000000000, mask is 0x3fffffff, and the 
routine returns -EIO.

For b43,       dev->dma_mask is 0xc265684800000001,
    dma_supported(dev, mask) is 0xc08b000000000000, mask is 0x77777777, and the 
routine returns 0.

Thus far I have not found what sets the low-order bit of dev->dma_mask. 
Suggestions are welcome.

These tests have all been with your patch that sets ARCH_ZONE_DMA_BITS to 30.

Larry