On Tue, 2023-02-14 at 13:12 +0100, Vincent Whitchurch wrote: > > Yes, Greg was initially totally opposed to the idea of putting platform > devices under PCI devices, but in his latest email he seemed to > allow it in some cases. It's still unclear if he'd be OK with a > "virtual PCI-to-platform bridge" though. And yes, adding platform > devices support like in this patch removes one layer and also eliminates > the disadvantage of having to wait for user space to specify a PCI ID > for the bridge device. Right. > > > + if (!dev->irq) > > > + return; > > > > > > > Does that mean platform devices don't have interrupts, or does that mean > > not all of them must have interrupts? > > They don't have interrupts via this driver. There isn't any standard > way for platform devices to handle interrupts since it it all depends on > what interrupt-parent is specified in the devicetree and how that is > implemented. Ah, OK. > > I'll note that this also would allow the device to send an MSI which > > feels a bit wrong? But I guess it doesn't really matter. > > We could avoid setting up the IRQ/MSI virtqueue when we know we're > dealing with platform devices. Not sure it matters then? > > So let me ask this: Conceptually, wouldn't the "right" way to handle > > this be a new virtio device and protocol and everything, with a new > > driver to handle it? I realise that would likely lead to quite a bit of > > code duplication, for now I just want to understand the concept here a > > bit better. > > Yes, that could be a way to do it. Or there could perhaps be some > feature bits indicating that only MMIO read/write/memset are allowed. Right. > > How much code would we actually duplicate? Most of virt-pci is dedicated > > to the mess of PCI MSI domains, bridges, etc. > > Probably not a huge amount, I can try to cook up a patch if you'd like. > But, besides the code duplication, I'm not sure if adding another new > virtio driver without a specification would be OK? Yeah ... let's not worry. Was mostly trying to understand it better. I'm not really bothered by it :) > > The limitation to a single device feels odd, and the fact that you have > > The limitation to a single device here is not a problem since one can > use simple-bus to instantiate any number of platform devices via the > devicetree. The devicetree at the end of this email shows how that > looks like. OK cool. > With a devicetree like the one below, using it shouldn't be all that > different from using the normal virt-pci except that the register ranges > and IRQ information are in the devicetree rather than coming via the > config space implementation in the virtio device. Makes sense. Thanks for all the answers & examples! Let's just leave it as is then :) johannes
