Hi, On Wed, Apr 06, 2011 at 08:47:34PM +0200, Samuel Ortiz wrote: > > > > What is a "MFD cell pointer" and why is it needed in struct device? > > > An MFD cell is an MFD instantiated device. > > > MFD (Multi Function Device) drivers instantiate platform devices. Those > > > devices drivers sometimes need a platform data pointer, sometimes an MFD > > > specific pointer, and sometimes both. Also, some of those drivers have been > > > implemented as MFD sub drivers, while others know nothing about MFD and just > > > expect a plain platform_data pointer. > > > > That sounds like a bug in those drivers, why not fix them to properly > > pass in the correct pointer? > Because they're drivers for generic IPs, not MFD ones. By forcing them to use > MFD specific structure and APIs, we make it more difficult for platform code > to instantiate them. I agree. What I do on those cases is to have a simple platform_device for the core IP driver and use platform_device_id tables to do runtime checks of the small differences. If one platform X doesn't use a platform_bus, it uses e.g. PCI, then you make a PCI "bridge" which allocates a platform_device with the correct name and adds that to the driver model. See [1] (for the core driver) and [2] (for a PCI bridge driver) for an example of what I'm talking about. > The timberdale MFD for example is built with a Xilinx SPI controller, and a > Micrel ks8842 ethernet switch IP. Forcing those devices into being MFD devices > would mean any platform willing to instantiate them would have to use the MFD > APIs. That sounds a bit artificial to me. do they share any address space ? If they do, then you'd need something to synchronize, right ? If they don't, then you just add two separate devices, they don't have to be MFD. > Although there is currently no drivers instantiated by both an MFD driver > and some platform code, Grant complaint about the Xilinx SPI driver moving > from a platform driver to an MFD one makes sense to me. I don't think so. That's not really an MFD device is it ? It's just two different IPs instantianted on the same ASIC/FPGA, right ? Unless they share the register space, IMHO, there's no need to make them MFD. [1] http://gitorious.org/usb/usb/blobs/dwc3/drivers/usb/dwc3/core.c [2] http://gitorious.org/usb/usb/blobs/dwc3/drivers/usb/dwc3/dwc3-haps.c -- balbi -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
