Re: [PATCH v4 1/5] drm/rockchip: Add basic drm driver

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Tuesday 23 September 2014 15:09:37 Mark yao wrote:
> On 2014年09月22日 23:54, Arnd Bergmann wrote:
> > On Monday 22 September 2014 17:15:06 Boris BREZILLON wrote:
> >>>> +
> >>>> +   /* TODO(djkurtz): fetch the mapping start/size from somewhere */
> >>>> +   mapping = arm_iommu_create_mapping(&platform_bus_type, 0x10000000,
> >>>> +                                      SZ_1G);
> >>>> +   if (IS_ERR(mapping)) {
> >>>> +           ret = PTR_ERR(mapping);
> >>>> +           goto err_config_cleanup;
> >>>> +   }
> >>>> +
> >>>> +   dma_set_coherent_mask(dev, DMA_BIT_MASK(32));
> >>> This is the default coherent mask. If you call this function, you
> >>> should normally check the return value, or call dma_set_mask first,
> >>> which you apparently don't do here, and in another place in this
> >>> patch.
> >> By "This is the default mask" do you mean it shouldn't be called at
> >> all ? Cause I ran into some trouble when not calling this in my
> >> atmel-hlcdc driver.
> > We used to get this wrong in the of_platform code, but it should
> > work now.
> >
> >> Actually, in my case the platform device is created by the MFD core
> >> which seems to let the coherent_dma_mask uninitialized.
> > That may well be different, but it seems like a good idea to allow
> > the MFD core to set this up as well.
> >
> > In general, we expect that devices that are capable of doing DMA
> > start with a 32-bit mask for both dma_mask and dma_coherent_mask,
> > and a driver that requires a smaller masks or wants a larger mask
> > has to call the appropriate interface to set these, and check the
> > return value.
> so I think we can use dma_set_mask_and_coherent(...) to set dma_mask and 
> dma_coherent_mark
> at the same time, and check the return value.

Yes, that would be good.

	Arnd
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