On 05/23/2014 02:36 PM, Thierry Reding wrote: > From: Thierry Reding <treding@xxxxxxxxxx> > > This commit introduces a generic device tree binding for IOMMU devices. > Only a very minimal subset is described here, but it is enough to cover > the requirements of both the Exynos System MMU and Tegra SMMU as > discussed here: > > https://lkml.org/lkml/2014/4/27/346 > > Signed-off-by: Thierry Reding <treding@xxxxxxxxxx> > --- > Apologies for the noise, but apparently I mistyped one of the email > addresses, should be fixed now. > > Changes in v2: > - add notes about "dma-ranges" property (drop note from commit message) > - document priorities of "iommus" property vs. "dma-ranges" property > - drop #iommu-cells in favour of #address-cells and #size-cells I think this is a mistake. address-cells/size-cells are for transactions flowing down the bus (from the CPU to date). Describing a connection from a device to an IOMMU is something completely different, and should therefore simply use an iommu-cells property to describe any necessary information. If we start re-using properties for different things in different contexts, how is anyone going to know what they mean, and how will conflicts be resolved. For example, what if there's a single HW module that both acts as a regular register bus with children (where address-cells/size-cells defines how transactions reach the children from the parent), and is also an IOMMU (where according to this binding proposal, address-cells/size-cells represent some aspect of the IOMMU feature). Using different properties for different things is the only sane way to keep different concepts separate. Another alternative would be to represent the single HW module as separate nodes in DT, but I think that will only make our lives harder, and where I've done that in the past, I've regretted it. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
