Reg: New MFD Driver for my PCIe Device

[Greg KH]

On Mon, Nov 08, 2021 at 11:27:45AM +0000, Lee Jones wrote:
> On Mon, 08 Nov 2021, Greg KH wrote:
> > On Mon, Nov 08, 2021 at 11:04:31AM +0000, Lee Jones wrote:
> > > On Mon, 08 Nov 2021, Kumaravel.Thiagarajan at microchip.com wrote:
> > > 
> > > > Dear Lee Jones,
> > > > 
> > > > I am Kumaravel Thiagarajan from Microchip, India and I am new to Linux Kernel development.
> > > > 
> > > > I am currently working on linux kernel driver for one of our PCIe based devices whose BAR 0 maps interface registers for a gpio controller, an OTP memory device controller and an EEPROM device controller into the host processor's memory space.
> > > > 
> > > > Based on earlier inputs from Linus Walleij, I have developed this as a multi-function device driver - First MFD driver (drivers/mfd) gets loaded for the PCIe device and then it spawns two child devices for OTP/EEPROM and GPIO separately.
> > > 
> > > You may wish to speak with Greg about your architectural decisions.
> > > 
> > > He usually dislikes the creation of platform devices from PCI ones.
> > 
> > Yes, that is NOT ok.
> > 
> > Platform devices are only for devices that are actually on a platform
> > (i.e. described by DT or other firmware types).
> 
> This is probably a bit of an over-simplification.  Lots of legitimate
> platform devices are actually described by DT et al.

We are in violent agreement here, that is what I was trying to say :)

> However, it is true that devices which reside on definite buses; PCI,
> USB, PCMIA, SCSI, Thunderbolt, etc should not spawn their children off
> as platform devices.

Agreed, that is not ok, as those are not what the platform device code
was designed for.

thanks,

greg k-h