Subject: Re: [resend/standalone PATCH v4] Add auxiliary bus support

From: Jason Gunthorpe <[email-masked]>
Date: Fri, 18 Dec 2020 19:36:08 -0400

On Fri, Dec 18, 2020 at 10:16:58PM +0100, Alexandre Belloni wrote:

> 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.

So, if mfd had a mfd_device and a mfd bus_type then drivers would need
to have both a mfd_driver and a platform_driver to bind. Look at
something like drivers/char/tpm/tpm_tis.c to see how a multi-probe
driver is structured

See Mark's remarks about the old of_platform_device, to explain why we
don't have a 'dt_device' today

> 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.

I think Thomas fixed that recently on x86 at least.. 

Having to put dummy irq chip drivers in MFD anything sounds scary :|

> 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.

Creating a platform_device to avoid restructuring the driver's probe
and device logic to be generic is a *really* horrible reason to use a
platform device.

Jason