On 5/25/2016 2:20 AM, Mark Rutland wrote: > On Tue, May 24, 2016 at 01:41:26PM -0700, Frank Rowand wrote: >> On 5/24/2016 10:41 AM, Mark Rutland wrote: >>> On Tue, May 24, 2016 at 06:39:20PM +0200, Christer Weinigel wrote: >>>> Document how to use devicetree aliases to assign a stable >>>> bus number to a spi bus. >>>> >>>> Signed-off-by: Christer Weinigel <christer@xxxxxxxxxxx> >>>> >>>> --- >>>> >>>> Trivial documentation change. >>>> >>>> Not having used devicetree that much it was surprisingly hard to >>>> figure out how to assign a stable bus number to a spi bus. Add a >>>> simple example that shows how to do that. >>>> >>>> Mark Cced as the SPI maintainer. Or should trivial documentation >>>> fixes like this be addressed to someone else? >>>> >>>> /Christer >>>> >>>> Documentation/devicetree/bindings/spi/spi-bus.txt | 10 ++++++++++ >>>> 1 file changed, 10 insertions(+) >>>> >>>> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt >>>> index 42d5954..c35c4c2 100644 >>>> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt >>>> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt >>>> @@ -94,3 +94,13 @@ SPI example for an MPC5200 SPI bus: >>>> reg = <1>; >>>> }; >>>> }; >>>> + >>>> +Normally SPI buses are assigned dynamic bus numbers starting at 32766 >>>> +and counting downwards. It is possible to assign the bus number >>>> +statically using devicetee aliases. For example, on the MPC5200 the >>>> +"spi@f00" device above is connected to the "soc" bus. To set its >>>> +bus_num to 1 add an aliases entry like this: >>> >>> As Mark Brown pointed out, this is very Linux-specific (at least in the >>> wording of the above). >> >> Yes, Linux-specific. So the Linux documentation of bindings is the >> correct place for it. > > I don't entirely agree. Which is not to say that I disagree as such, but > rather that this is not a black-and-white affair. > > While bindings do happen to live in the kernel tree, we try to keep them > separate from Linux internals or Linux API details that are outside of > the scope of the HW/kernel interface. There are certainly reasons to > describe Linux-specific bindings (e.g. things under /chosen). Where should this be documented? > Mark Brown's comments imply that there is a better mechanism which does > not rely on this binding, so even if we must retain support for it in > Linux for legacy reasons, documenting it as a binding is not necessarily > in anyone's best interest. If we want to document it, we may want to > mark it as deprecated, with a pointer to better alternatives. Lack of documentation and bad documentation are a MAJOR problem for devicetree. Refusing to accept documentation of existing behavior makes no sense to me. >>> Generally, aliases are there to match _physical_ identifiers (e.g. to >>> match physical labels for UART0, UART1, and on). >>> >>> I'm not sure whether that applies here. >> >> The code and behavior is in the Linux kernel. It should be visible in >> the documentation instead of being a big mystery of how it works. > > As above, I don't entirely agree. Mindlessly documenting existing Linux > behaviour can have the unfortuante effect of moving people towards the > wrong tool for the job. > > Thanks, > Mark. > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
