Messages in this thread |  | | Subject | Re: [PATCH v2 00/16] ARM: support for ICP DAS LP-8x4x (with dts) | From | Sergei Ianovich <> | Date | Sun, 15 Dec 2013 01:55:46 +0400 |
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On Sat, 2013-12-14 at 22:03 +0100, Arnd Bergmann wrote: > On Friday 13 December 2013, Sergei Ianovich wrote: > > I've also decided not to create a single mfd device for > > machine-specific devices. Instead each type is supported by a separate > > driver in respective subsystem. It was tempting to hardcode all the > > constants in one source file, but that requires ugly initialization. > > The taken way produces much cleaner code. > > I think you should at least change the DT representation for the FPGA > to show one device as the actual FPGA and attach children to that, > multiple indirection levels if necessary. > > I suspect that the fpga is on some external-bus port with a specific > chip-select, so I would model this as > > extbus { > compatible = "simple-bus"; > #address-cells = <1>; > #size-cells = <1>; > /* bus addresses 0-0xfffff mapped to 0x17000000 */ > ranges = <0 0x17000000 0x100000>; > interrupt-parent = <&fpga-irq>; > > fpga-irq: irq@6 { > regs = <6 16>; /* translated addresses > ... > }; > > fgpa-bus { > #address-cells = <1>; > #size-cells = <1>; > ranges; > > serial@9050 { > ... > }; > }; > }; > > I also think you don't need to make the devices quite as fine-grained > here but instead group things together more. I would probably indeed > put everything that is not on one of the slots into a common device, > including the irqchip.
There are basically 2 options: one-for-all mfd device and one-for-one device drivers.
MFD pros: * easy to add into the tree (one file) * easy config (one option)
Separate devices * easy to support devices as respective subsystems evolve * easy to add new feature without breaking existing ones. Eg. it may make sense to provide industrial IO interface on analog IO devices * possible to have fine-grained configuration (eg. SRAM in kernel, serial and slot as modules) * proper device tree serves as a datasheet for the machine, so anyone who needs to work on it will have a decent view of the internals
I believe long-term benefits of separate devices outweigh immediate effects of an MFD. However, I certainly don't see the big picture and will accept your decision. Please make one.
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