Hi Will, On 4/18/2013 12:01 PM, Will Deacon wrote: > On Tue, Apr 16, 2013 at 07:18:42PM +0100, Olav Haugan wrote: >> On 4/15/2013 6:13 AM, Will Deacon wrote: >>> If so, doesn't that strongly tie your video driver to the SMMU? >> >> Isn't this more or less what you are doing in DT where you associate >> specific devices with an IOMMU (mmu-masters)? > > No. The device-tree describes the *hardware*, as per usual. The StreamIDs > are fixed properties of the SoC and we can't change them from Linux, so we > describe all of the StreamIDs upstream of each SMMU so that we can program > the thing. There's no way to generic way to discover them. I meant that you are putting phandles to bus masters in the device tree that use/need the SMMU for VA2PA translation. Doesn't this put a dependency on the bus master devices? How will this work? Lets say that we have a device during bootup that needs to use the SMMU (such as a display processor [DP]). Don't you have cyclic dependency? The SMMU device needs the DP device (phandle) but the DP device needs the SMMU to initialize its device driver? >>> This seems to be where we differ. My anticipated use-case is that a domain >>> is allocated, which defines an empty address space. Masters are then >>> attached to the domain by passing their struct device, so this may >>> correspond to a DMA controller or a video core, in your case. The context >>> bank is allocated dynamically when the first device is added to the >>> domain, and then it is subsequently shared between all the masters in that >>> domain. >> >> I feel that there are some limitation with this. Maybe you can address >> the following: >> >> 1) What if you want two context banks in one domain (shared page table)? > > Why would a page table shared between devices require multiple context > banks? Multiple SMRs and S2CRs, sure, but they would ultimately point at the > same context bank (and hence same address space). What if you want to have 2 different VMID's being generated? Also, what about TLB management? If I have two context banks I can invalidate only entries associated with 1 of the context banks (if VMID differ for the two context banks). >> 2) What if a master (device) needs to use 2 or more context banks? > > If a master needs to be in two address spaces at once, then it will need to > attach it's StreamIDs to different domains. You can't place a single > StreamID in two address spaces (this is an architectural constraint). Yes, you would have a separate domain. I am just wondering how I would model this in DT using the bindings that you are proposing? How does it work? The bindings specify bus masters to StreamIDs. So if I call attach with the master device you will allocate a context bank and program the StreamIDs as specified in the DT. So now if I want to have another context bank associated with the same master device what do I do? I call into attach with a new domain but with the same master device but the master device is already attached to a context/domain. Thanks, Olav Haugan -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
