On Mon, Oct 21, 2013 at 09:05:44PM +0100, Stephen Warren wrote: > On 10/21/2013 12:44 AM, Guenter Roeck wrote: > > On 10/20/2013 04:11 PM, Russell King - ARM Linux wrote: > >> On Sun, Oct 20, 2013 at 10:26:54PM +0100, Stephen Warren wrote: > >>> The only thing we've really moved out of the kernel is the exact IDs of > >>> which GPIOS, interrupts, I2C/SPI ports the devices are connected to; the > >>> simple stuff not the hard stuff. The code hasn't really been simplified > >>> by DT - if anything, it's more complicated since we now have to parse > >>> those values from DT rather than putting them into simple > >>> data-structures. > >> > >> Here's my random thoughts this evening on DT, orientated mostly on a > >> problem area I've been paying attention to recently. > >> > >> In some ways, DT has made things much harder. I don't know whether > > > > On the other side, DT has made some things much simpler. > > > > Problem case: Chip A's interrupt pin is connected to gpio pin of chip B. > > Chip B's interrupt pin is connected to a gpio pin on chip C. Chip C's > > interrupt pin is connected to the interrupt controller. Chips B and C > > are multi-function FPGAs. Exact gpio pins used vary from board to board. > > > > With DT, this relationship is easy to describe, and none of the chip > > drivers > > really needs to know what is connected to what. Without DT, it would be > > much more complex. > > I thought that was very easy with board files. For every chip that gets > instantiated, you tell it which base IRQ ID to use. For every chip that > outputs a IRQ, you tell it which IRQ ID that signal is, simply by adding > the recipient chip's IRQ base and an offset. That seems very simple. If > you don't want to add the base/offset together, we could always have > invented some lookup table similar to what regulators had, and pinctrl > has now, which says for each (device name, IRQ name/number) output, > here's the (device name, IRQ name/number) of the associated input. Well, DT has certainly increased the level of dynamicity within the kernel. I for one consider not having to rely on a fixed IRQ or GPIO base per-chip a good thing. Deferred probing is a very powerful yet extremely simple tool that was created as part of the DT conversion effort. There is obviously much more that can be done, but I think that we have come a long way. But as you said, that could all have been done even with board files. Thierry
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