On Fri, Dec 18, 2020 at 1:17 PM Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx> wrote: > > On 18/12/2020 16:58:56-0400, Jason Gunthorpe wrote: > > On Fri, Dec 18, 2020 at 08:32:11PM +0000, Mark Brown wrote: > > > > > > So, I strongly suspect, MFD should create mfd devices on a MFD bus > > > > type. > > > > > > Historically people did try to create custom bus types, as I have > > > pointed out before there was then pushback that these were duplicating > > > the platform bus so everything uses platform bus. > > > > Yes, I vaugely remember.. > > > > I don't know what to say, it seems Greg doesn't share this view of > > platform devices as a universal device. > > > > Reading between the lines, I suppose things would have been happier > > with some kind of inheritance scheme where platform device remained as > > only instantiated directly in board files, while drivers could bind to > > OF/DT/ACPI/FPGA/etc device instantiations with minimal duplication & > > boilerplate. > > > > And maybe that is exactly what we have today with platform devices, > > though the name is now unfortunate. > > > > > I can't tell the difference between what it's doing and what SOF is > > > doing, the code I've seen is just looking at the system it's running > > > on and registering a fixed set of client devices. It looks slightly > > > different because it's registering a device at a time with some wrapper > > > functions involved but that's what the code actually does. > > > > SOF's aux bus usage in general seems weird to me, but if you think > > it fits the mfd scheme of primarily describing HW to partition vs > > describing a SW API then maybe it should use mfd. > > > > The only problem with mfd as far as SOF is concerned was Greg was not > > happy when he saw PCI stuff in the MFD subsystem. > > > > But then again, what about non-enumerable devices on the PCI device? I > feel this would exactly fit MFD. This is a collection of IPs that exist > as standalone but in this case are grouped in a single device. > > Note that I then have another issue because the kernel doesn't support > irq controllers on PCI and this is exactly what my SoC has. But for now, > I can just duplicate the irqchip driver in the MFD driver. > > > This whole thing started when Intel first proposed to directly create > > platform_device's in their ethernet driver and Greg had a quite strong > > NAK to that. > > Let me point to drivers/net/ethernet/cadence/macb_pci.c which is a > fairly recent example. It does exactly that and I'm not sure you could > do it otherwise while still not having to duplicate most of macb_probe. > This still feels an orthogonal example to the problem auxiliary-bus is solving. If a platform-device and a pci-device surface an IP with a shared programming model that's an argument for a shared library, like libata to house the commonality. In contrast auxiliary-bus is a software model for software-defined sub-functionality to be wrapped in a driver model. It assumes a parent-device / parent-driver hierarchy that platform-bus and pci-bus do not imply.
