Hi Tomasz,

On Friday 12 Aug 2016 16:31:47 Tomasz Figa wrote:

On Tue, Aug 9, 2016 at 7:49 AM, Sricharan R wrote:

quoted

From: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

The of_configure_dma() function configures both the DMA masks and ops.
Moving DMA ops configuration to probe time would thus also delay
configuration of the DMA masks, which might not be safe. To avoid issues

Do we know any example cases when it might be unsafe? I think we kind
of rely on the fact that DMA mapping (and so DMA masks as well) is not
used before probing the device anyway, because we let the IOMMU
attachment happen at probe time, which essentially makes any earlier
attempts to use DMA mapping on such device incorrect.

I don't know of any such situation, but (if I remember correctly) when I 
discussed the IOMMU rework with Arnd Bergman and Will Deacon there was a 
concern that someone, somewhere was relying on the mask being set early.

I personally would like to drop this patch, but it might be difficult to 
ensure this wouldn't cause a regression. There should certainly be no DMA 
mapping created before IOMMU attachment, but the DMA mask could possibly be 
used somewhere else.

-- 
Regards,

Laurent Pinchart