Re: [PATCH net] macmace: Set platform device coherent_dma_mask

[Michael Schmitz]

Hi Geert,

Am 04.05.2018 um 19:24 schrieb Geert Uytterhoeven:
> Hi Michael,
> 
>>> Yes, that would be useful.  The other assumption could be that
>>> platform devices always allow an all-0xff dma mask.
>>
>> That's not always true (Atari NCR5380 SCSI and floppy would use a 24
>> bit DMA mask). We use bounce buffers allocated from a dedicated lowmem
>> pool there currently, and for all I know don't use the DMA API yet.
>>
>> I bet that is a rare exception though. Setting the default DMA mask
>> for platform devices to all-0xff and letting the few odd drivers force
>> a different setting seems the best way forward.
> 
> I'd say that's usually a property of the platform, not of the device?

Right - I was thinking 'm68k' as platform, not a particular machine like
Mac or Falcon (the 24 bit mask only applies to that particular model
anyway).

> So IMHO it belongs in the platform code, not in the device driver code.

OK - let's have a default mask of 64 bit, and allow machine specific
platform_init() to override using a new helper function.

Cheers,

	Michael

> Gr{oetje,eeting}s,
> 
>                         Geert
>