On 2/19/2015 8:40 AM, Frank Rowand wrote: > On 2/19/2015 6:41 AM, Pantelis Antoniou wrote: >> Hi Frank, >> >>> On Feb 19, 2015, at 04:08 , Frank Rowand <frowand.list@xxxxxxxxx> wrote: >>> >>> On 2/18/2015 6:59 AM, Pantelis Antoniou wrote: >>>> Implement a method of applying DT quirks early in the boot sequence. >>>> >>>> A DT quirk is a subtree of the boot DT that can be applied to >>>> a target in the base DT resulting in a modification of the live >>>> tree. The format of the quirk nodes is that of a device tree overlay. >>> >>> The use of the word "quirk" is a different mental model for me than what >>> this patch series appears to be addressing. I would suggest totally >>> removing the word "quirk" from this proposal to avoid confusing the >>> mental models of future generations of kernel folks. >>> >> >> Naming things is hard to do. Suggestions? > > You are inviting me to bikeshed. I'll leave that to you. > >> >>> What this patch series seems to be proposing is a method to apply DT >>> overlays as soon as unflatten_device_tree() completes. In other words, >>> making the device tree a dynamic object, that is partially defined by >>> the kernel during boot. Well, to be fair, the kernel chooses among >>> several possible alternatives encoded in the DT blob. So the device >>> tree is no longer a static object that describes the hardware of the >>> system. It may not sound like a big deal, but it seems to me to be >>> a fundamental shift in what the device tree blob is. Something that >>> should be thought about carefully and not just applied as a patch to >>> solve a point problem. >>> >> >> There is a fundamental shift going on about what hardware is. It is nowhere >> as static as it used to be. It is time for the kernel to keep up. > > Run time overlays do that. > > The problem you seem to be dealing with here is that you want a single > DT blob that can be installed on many different _physical_ boards. > > >> >>> The stated use of this proposal is to create dynamic DT blobs that can >>> describe many similar variants of a given system instead of creating >>> unique DT blobs for each different system. >>> >> >> Yes. >> >>> I obviously have not thought through the architectural implications yet, >>> but just a quick example. One of the issues we have been trying to fix >>> is device tree validation. The not yet existent (except as a few proof >>> of concept attempts) validator would need to validate a device tree >>> for each dynamic variant. Probably not a big deal, but an example of >>> the ripple effects this conceptual change implies. >>> >> >> I don’t see what the big problem with the validator is. The ‘quirk’ >> are easily identified by the presence of the __overlay__ nodes and >> the validator can apply each overlay and perform the validation check >> at each resultant tree. > > I said "not a big deal". I was trying to make people think about the > bigger picture. Defending that this is a non-issue for the validator > is totally missing my point. Step back and think architecturally > about the big picture. I do _not_ know if this is a problem, but > they will be ripples from this proposal. oops: there will be ripples from this proposal. > >> >>> A second function that this patch is proposing is a method to enable >>> or disable devices via command line options. If I understand >>> correctly, this is meant to solve a problem with run time overlays >>> that require disabling a device previously enabled by the DT blob. >>> If so, it seems like it could easily be implemented in a simpler >>> generic way than in the board specific code in this patch series. >>> >> >> Disabling a device is the most common case, but other options are desired >> too. For instance changing OPPs by a command line option, etc. > > The device tree is supposed to describe what the hardware is. Why would > you want a command line option to change what OPPs are possible for the > hardware? > >> >>> I share the concerns that Mark Rutland has expressed in his comments >>> about this series. >>> >>> < snip > >>> >>> I have read through the patches and will have comments on the code >>> later if this proposal is seen as a good idea. >>> >> >> OK >> >>> -Frank >> >> Regards >> >> — Pantelis >> >> > -- 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
