On Tue, May 10, 2016 at 01:02:08PM +0200, Ulf Hansson wrote: > + Arnd > > [...] > > >> >> Solution > >> >> ======== > >> >> This is very similar to the MMC pwrseq behavior so the idea is to: > >> >> 1. Move MMC pwrseq drivers to generic place, > >> > > >> > You can do that, but I'm going to NAK any use of pwrseq bindings outside > >> > of MMC. I think it is the wrong way to do things. The DT should describe > >> > >> Huh, I didn't know that was your view of the mmc pwrseq bindings. Why > >> didn't you NAK them before? > > > > Unfortunately, either I missed it or it was a time I couldn't spend much > > time on reviews. > > Okay, I guess it's common issue among maintainers. The problem with DT > is that it gets really hard to be fixed up later. :-) > > > > >> > the devices. If they happen to be "simple" then the core can walk the > >> > tree and do any setup. For example, look for "reset-gpios" and toggle > >> > that GPIO. There is no need for a special node. > >> > > >> >> 2. Extend the pwrseq-simple with regulator toggling, > >> >> 3. Add support to USB hub and port core for pwrseq, > >> > > >> > We discussed this for USB already[1] and is why we defined how to add > >> > USB child devices. The idea is not to add pwrseq to that. > >> > >> I am not familiar with the USB discussion. > >> > >> Still, let me give you some more background to the mmc pwrseq. The > >> idea from the mmc pwrseq bindings comes from the power-domain DT > >> bindings, as I thought these things were a bit related. > >> In both cases they are not directly a property of the device, but more > >> describing a HW dependency to allow the device to work. > > > > I could see this as a board level power domain. However the difference > > is we are not generally exposing internal SOC details the same way as > > board level components. Perhaps we could extend power domains to board > > level, but that is not what was done here. > > > >> One could probably use a child node instead of a phandle, but that > >> wasn't chosen back then. Of course you are the DT expert, but could > >> you perhaps tell me why a child node is better for cases like this? > > > > If there is a control path hierarchy, then we try to model that in DT > > with child nodes. In cases of SDIO and USB, there is a clear hierarchy. > > Ignoring the discovery ordering problem, we already have defined ways to > > describe GPIO connections, regulators, etc. to devices. Describing those > > things separately from the device to solve a particular issue that is > > really a kernel limitation is what I don't like. > > Okay, I see. > > To move forward in trying to make mmc pwrseq a generic pwrseq, could > we perhaps allow both cases? > > In the mmc case, there are already deployed bindings so we need to > cope with these by using the phandle option, but for USB etc we could > force the child node option. > As long as we agree that we keep using a compatible string for the > child node as well, both options should be able to co-exist and we > should probably be able to managed them both from a common pwrseq > driver framework. > > Although, I do remember from an older conversations around some of > mine submission for the mmc pwrseq code, that some people (maybe > Arnd?) wasn't keen on adding a new framework for this. Perhaps that > has changed? > All, how we move on for this? 1. Using a generic driver to manage both mmc and USB (and further subsystem), USB and further subsystem do not use pwrseq node in dts. 2. USB creates the similar driver under drivers/usb for its own use. Which one do you prefer, thanks. -- Best Regards, Peter Chen -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
