[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [RFC v1 5/5] xen/arm: add SCI mediator support for DomUs
Hi Julien, On Fri, Dec 24, 2021 at 02:30:50PM +0100, Julien Grall wrote: > Hi, > > On 23/12/2021 20:06, Stefano Stabellini wrote: > > On Wed, 22 Dec 2021, Stefano Stabellini wrote: > > > # Future Ideas > > > > > > A great suggestion by Julien is to start supporting the dom0less partial > > > device tree format in xl/libxl as well so that we can have a single > > > "device_tree" option in dom.cfg instead of 4 (device_tree, iomem, irqs, > > > dtdev). > > > > > > Even with that implemented, the user has still to provide a partial dtb, > > > xen,reg and xen,path. I think this is a great step forward and we should > > > do that, if nothing else to make it easier to switch between dom0less > > > and normal domU configurations. But the number of options and > > > information that the user has to provide is still similar to what we > > > have today. > > > > I have just realized that if we start to parse the partial DTB in > > xl/libxl the same way that we do for dom0less guests (parse "xen,path", > > "xen,reg", and "interrupts", making dtdev, irqs and iomem optional) > > actually we can achieve the goal below thanks to the combination: > > "xen,path" + "xen,force-assign-without-iommu". > > > > In other words, with dom0less we already have a way to specify the link > > to the host node even if the device is not a DMA master. We can do that > > by specifying both xen,path and xen,force-assign-without-iommu for a > > device. > > > > This is just FYI. I am not suggesting we should introduce dom0less-style > > partial DTBs in order to get SCMI support in guests (although it would > > be great to have). I think the best way forward for this series is one > > of the combinations below, like a) + d), or a) + c) > > I strongly prefer a) + c) because a warning is easy to miss/ignore. At least > with the extra property the user made an action to think about it and agree > that this is the way do it. > > It is also easier to spot if we ask the user to provide the configuration > file. > Let me share my thoughts about c), which is: c) require force-assign-without-iommu="true" in dom.cfg Adding this parameter to domain config means removing xen,force-assign-without-iommu param from partial DTB. This will affect dom0less configuration, which I can't test for now without extra effort. What I suggest is to implement a) + d) in this patch series, which is: a) extend dtdev to cover all devices, including non-DMA masters d) or print a warning like: "WARNING: device assignment safety for device XXX cannot be verified. Please make sure XXX is not a DMA mastering device." And introduce a) + c) with the next patch series where dom0less scmi support will be done. Maybe leave a comment in code that force-assign-without-iommu config parameter should be implemened. What do you think about this? -- Best regards, Oleksii.
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