Messages in this thread | | | Subject | Re: [BISECTED REGRESSION] b43legacy broken on G4 PowerBook | From | Larry Finger <> | Date | Thu, 6 Jun 2019 14:26:19 -0500 |
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On 6/6/19 6:43 AM, Christoph Hellwig wrote: > On Thu, Jun 06, 2019 at 08:57:49PM +1000, Benjamin Herrenschmidt wrote: >>> Wow... that's an odd amount. One thing we could possibly do is add code >>> to limit the amount of RAM when we detect that device.... >> >> Sent too quickly... I mean that *or* force swiotlb at 30-bits on those systems based >> on detecting the presence of that device in the device-tree. > > swiotlb doesn't really help you, as these days swiotlb on matters for > the dma_map* case. What would help is a ZONE_DMA that covers these > devices. No need to do the 24-bit x86 does, but 30-bit would do it. > > WIP patch for testing below: > > diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h > index b8286a2013b4..7a367ce87c41 100644 > --- a/arch/powerpc/include/asm/page.h > +++ b/arch/powerpc/include/asm/page.h > @@ -319,6 +319,10 @@ struct vm_area_struct; > #endif /* __ASSEMBLY__ */ > #include <asm/slice.h> > > +#if 1 /* XXX: pmac? dynamic discovery? */ > +#define ARCH_ZONE_DMA_BITS 30 > +#else > #define ARCH_ZONE_DMA_BITS 31 > +#endif > > #endif /* _ASM_POWERPC_PAGE_H */ > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c > index cba29131bccc..2540d3b2588c 100644 > --- a/arch/powerpc/mm/mem.c > +++ b/arch/powerpc/mm/mem.c > @@ -248,7 +248,8 @@ void __init paging_init(void) > (long int)((top_of_ram - total_ram) >> 20)); > > #ifdef CONFIG_ZONE_DMA > - max_zone_pfns[ZONE_DMA] = min(max_low_pfn, 0x7fffffffUL >> PAGE_SHIFT); > + max_zone_pfns[ZONE_DMA] = min(max_low_pfn, > + ((1UL << ARCH_ZONE_DMA_BITS) - 1) >> PAGE_SHIFT); > #endif > max_zone_pfns[ZONE_NORMAL] = max_low_pfn; > #ifdef CONFIG_HIGHMEM >
I am generating a test kernel with this patch.
FYI, the "free" command on my machine shows 1.5+ G of memory. That likely means I have 2G installed.
I have tested a patched kernel in which b43legacy falls back to a 31-bit DMA mask when the 32-bit one failed. That worked, but would likely kill the x86 version. Let me know if think a fix in the driver rather than the kernel would be better. I still need to understand why the same setup works in b43 and fails in b43legacy. :(
Larry
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