On Wed, Aug 27, 2014 at 11:05:29AM +0200, Geert Uytterhoeven wrote: > On Wed, Aug 27, 2014 at 10:55 AM, Maxime Ripard > <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > >> >> Is simplefb something that should be in the device tree distinctly in > >> >> the first place - shouldn't it be a subset of the functionality of the > >> >> video nodes? It's the same hardware being driven differently. > >> > > >> > Therorically, yes, but that would mean knowing beforehand what the > >> > final binding will look like, even before submitting the driver. Since > >> > the bindings are always reviewed, and most of the time changed > >> > slightly, that wouldn't work very well with the DT as a stable ABI > >> > policy I guess. > >> > >> If you don't know how the bindings for a device will look like at the time of > >> writing your DTS, you're always screwed, whether you add a simpefb > >> node or not. > >> > >> If you know how the bindings look like, just add the device, with an extra > >> "linux,simplefb" compatibility value. > >> If you don't know how the bindings look like, do your utter best in > >> guessing. Your DTS must be amended later anyway, either because > >> you guessed wrong[*] (in case you added a node to have simplefb > >> working), or because you have to add a real device node (in case you > >> didn't add one for simplefb). > > > > Let's be conservative and consider the case where we would guess > > wrong. > > > > If we just rely on a simplefb node, when reviewing and integrating the > > "new" bindings to describe accureately the various IPs involved in the > > display path, we would obviously create new compatibles for > > them. Since it's new compatibles, we can come up with any binding we'd > > like, without have to consider the backward compatibility, since it's > > a new binding. > > > > Then, we just remove the simplefb, all is good. > > I would keep the simplefb compatible value. Else you break compatibility > with old kernels that don't have your new driver. Yes, true. Since the simplefb will be injected by u-boot, it will be there anyway. -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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