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? > 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. > 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. > 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. > 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
