Re: [PATCH] powerpc: enable a 30-bit ZONE_DMA for 32-bit pmac

[Larry Finger <Larry.Finger@lwfinger.net>]

On 6/14/19 2:15 PM, Aaro Koskinen wrote:
> Hi,
> 
> On Fri, Jun 14, 2019 at 09:24:16AM +0200, Mathieu Malaterre wrote:
>> On Thu, Jun 13, 2019 at 10:27 AM Christoph Hellwig <hch@lst.de> wrote:
>>> With the strict dma mask checking introduced with the switch to
>>> the generic DMA direct code common wifi chips on 32-bit powerbooks
>>> stopped working.  Add a 30-bit ZONE_DMA to the 32-bit pmac builds
>>> to allow them to reliably allocate dma coherent memory.
>>>
>>> Fixes: 65a21b71f948 ("powerpc/dma: remove dma_nommu_dma_supported")
>>> Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>> ---
>>>   arch/powerpc/include/asm/page.h         | 7 +++++++
>>>   arch/powerpc/mm/mem.c                   | 3 ++-
>>>   arch/powerpc/platforms/powermac/Kconfig | 1 +
>>>   3 files changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
>>> index b8286a2013b4..0d52f57fca04 100644
>>> --- a/arch/powerpc/include/asm/page.h
>>> +++ b/arch/powerpc/include/asm/page.h
>>> @@ -319,6 +319,13 @@ struct vm_area_struct;
>>>   #endif /* __ASSEMBLY__ */
>>>   #include <asm/slice.h>
>>>
>>> +/*
>>> + * Allow 30-bit DMA for very limited Broadcom wifi chips on many powerbooks.
>>
>> nit: would it be possible to mention explicit reference to b43-legacy.
>> Using b43 on my macmini g4 never showed those symptoms (using
>> 5.2.0-rc2+)
> 
> According to Wikipedia Mac mini G4 is limited to 1 GB RAM, so that's
> why you don't see the issue.

He wouldn't see it with b43. Those cards have 32-bit DMA.

Larry