On Tue, Jun 30, 2020 at 08:32:45AM -0300, Jason Gunthorpe wrote: > On Tue, Jun 30, 2020 at 11:31:41AM +0100, Mark Brown wrote: > > On Mon, Jun 29, 2020 at 07:59:59PM -0300, Jason Gunthorpe wrote: > > > > What are we supposed to do with things like PCI attached FPGAs and ASICs > > > > in that case? They can have host visible devices with physical > > > > resources like MMIO ranges and interrupts without those being split up > > > > neatly as PCI subfunctions - the original use case for MFD was such > > > > ASICs, there's a few PCI drivers in there now. > > > Greg has been pretty clear that MFD shouldn't have been used on top of > > > PCI drivers. > > The proposed bus lacks resource handling, an equivalent of > > platform_get_resource() and friends for example, which would be needed > > for use with physical devices. Both that and the name suggest that it's > > for virtual devices. > Resource handling is only useful if the HW has a hard distinction > between it's functional blocks. This scheme is intended for devices > where that doesn't exist. The driver that attaches to the PCI device > and creates the virtual devices is supposed to provide SW abstractions > for the other drivers to sit on. > I'm not sure why we are calling it virtual bus. The abstraction that the PCI based MFDs (and FPGAs will be similar, they're just dynamic MFDs to a good approximation) need is to pass through MMIO regions, interrupts and so on which is exactly what the platform bus offers. The hardware is basically someone taking a bunch of IPs and shoving them behind the MMIO/interrupt regions of a PCI device. > > The reason the MFDs use platform devices is that they end up having to > > have all the features of platform devices - originally people were > > making virtual buses for them but the code duplication is real so > > everyone (including Greg) decided to just use what was there already. > Maybe Greg will explain why he didn't like the earlier version of that > stuff that used MFD AFAICT Greg is mostly concerned about the MFDs that aren't memory mapped, though some of them do use the resource API to pass interrupts through.
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