Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH v4 1/5] drm/rockchip: Add basic drm driver | Date | Mon, 22 Sep 2014 17:54:42 +0200 |
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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.
Arnd
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