On Tue, Apr 08, 2014 at 05:02:37PM +0200, Laurent Pinchart wrote: > On Tuesday 08 April 2014 15:43:22 Joerg Roedel wrote: > > Who is "someone" in this case? > > That's exactly the problem :-) The ARM DMA API implementation doesn't care who > that "someone" is. Existing implementations call those functions either from > the bus masters device drivers (in which case the drivers need to be IOMMU- > aware, even if they use the DMA API and don't need to handle the IOMMU > directly) or from the IOMMU drivers (in which case the bus masters device > drivers don't have to care about the IOMMU, but without a way for drivers to > handle the IOMMU directly when they need to). Possible other candidates are > core IOMMU code or bus code. That doesn't sound very transparent for the device drivers. All what you describe above (attaching a device to its default domain for DMA-API) should happen in the IOMMU driver. For the device driver it should make no difference if there is an IOMMU or not. > If we call arm_iommu_attach_device() from the IOMMU driver to get default > transparent IOMMU handling, the function will then attach the device to the > default domain with a call to iommu_attach_device(). If you have to call a function it is not transparent anymore. > If a driver needs to handle the IOMMU directly, should it start by > detaching the device from the ARM IOMMU domain ? We would need to be > very careful with the assumptions made by the different layers, as > they might not support a driver attaching a new domain to a device > that already has a domain attached. I'd feel more comfortable with > avoiding to attach the default domain to the device in the first > place, but that might not be easily doable. The way this is solved by others is that iommu_attach_device() automatically detaches the device from its default (DMA-API) domain and attach it to the device drivers own domain. On iommu_detach_device() the device is attached back to the default domain. Joerg -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
