Messages in this thread | | | Date | Fri, 26 Jul 2013 09:45:51 -0400 | From | Jason Cooper <> | Subject | Re: [Ksummit-2013-discuss] DT bindings as ABI [was: Do we have people interested in device tree janitoring / cleanup?] |
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On Fri, Jul 26, 2013 at 02:38:02PM +0100, Russell King - ARM Linux wrote: > On Fri, Jul 26, 2013 at 09:27:09AM -0400, Jason Cooper wrote: > > On Fri, Jul 26, 2013 at 03:09:29PM +0200, Richard Cochran wrote: > > > Unless I totally misunderstood, the thread is talking about letting > > > established bindings change with each new kernel version. I am > > > opposed to that. > > > > > > Of course, a user may want to change the values of his MAC addresses, > > > if he needs to. But he should never have to change *how* he specifies > > > those addresses. > > > > The other dynamic change that bears mentioning here is attributes which > > have been configured by the bootloader. For example, in mvebu, we have > > the Schrodinger's Cat register. It allows you to reconfigure the base > > address of the registers from *within* that register range. If the > > bootloader does this, the DT needs to be updated to reflect the current > > hardware configuration. Otherwise, the kernel is stuck poking around at > > memory addresses hoping to find something sane. > > > > But this falls into the same category as you mentioned, but outside of > > chosen {};. > > No, this falls within the remit of "describing the hardware" and it is > certainly something that is free to change.
We agree, I was just highlighting that attributes outside of chosen can and need to be rewritten by the bootloader.
> What should not "change" once a kernel is the method by which hardware is > described in DT. "change" there in the sense that how it was described by > kernel 3.X should still be accepted by 3.X+n, even if 3.X+n comes up with > a much better way to describe it. > > The actual data associated with those descriptions is free to change in > whatever way is necessary if the hardware itself changes due to things > being programmed differently. > > Think of it as the difference between the design of an interface, and the > interface being used. We don't mandate that the write() syscall shall > always be called for fd=1 with length=5 and bytes "Hello" in the buffer. > We mandate that the write() syscall shall be passed an integer fd, a > buffer pointer, and a length and we don't change that ever. > > Think of "a better way to describe it" as introducing the writev() syscall > to supplement write() so that applications can do writes from scattered > memory locations. We don't get rid of the write() syscall - we add to > the ABI that's already there leaving the existing interfaces with exactly > the same semantics, so that all the existing stuff continues to work as-is.
Yes, the manner in which the bootloader writes the changes should adhere to the binding. In my example, it shouldn't replace the reg property with reg-mod. It should just change the addresses to reflect the current state of the hardware the kernel will see.
thx,
Jason.
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