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Now, however, they do with the co= re > > > power domain. > > >=20 > > > This happens to work on most systems due to DSI already being out of > > > reset when booting the kernel, but on Tegra114 Dalmore, this is not t= he > > > case and causes the system to hang during boot. > > >=20 > > > Ownership of the reset line is no longer a problem with reset > > > acquire/release semantics, so control the DSI reset unconditionally > > > from the DSI driver (possibly in addition to the power domain driver)= . > > > The device tree bindings already require the reset and it is present > > > on all platforms, so this is safe to do. > >=20 > > That seems backwards to me. The whole point of doing this via power > > domains was because it's explicitly not safe to toggle that reset line > > outside of the powergate switching sequence. If you're referring to the MBIST workaround, unless I misremember, it=20 doesn't mean the reset cannot be used outside the powergate sequence,=20 just that it has to be used within in. > >=20 > > Also, the power domain code paths are supposed to work regardless of > > whether the DSI was already out of reset or not. If that's not working > > right now, I think that would qualify as a bug in the power domain code > > rather than the DSI driver. > >=20 > > Shouldn't this be fixed at the powergate level? My recollection is that > > DSI is tightly coupled to the display powergates, though it's been a > > long time. Do we maybe need to reflect that in DT? There's a TODO in > > tegra114.dtsi that seems to indicate that we're missing DIS and DISB > > powergate implementations, so maybe that's where we should start to try > > and resolve this. >=20 > Looking at this a bit more, pd_core doesn't seem to make sense for DSI. > Basically what that does, semantically, is claim that there's a power > domain responsible for powering up and down the device, but in reality > it doesn't to squat. Doesn't that reasoning apply for every device? Technically, pd_core=20 corresponds to the core power rail. DSI is powered from it.. we=20 certainly haven't always had an expectation that the power domain=20 provider handles resets for the device. On Tegra114 it looks like DSI indeed is in the DIS domain so that would=20 handle it, but on Tegra20/Tegra30 that isn't the case (even if those=20 device seem to be working right now anyway). >=20 > Does the hang you observe go away if you remove the power-domains > property for DSI? pd_core should probably be removed for both display > controllers and HDMI as well. Probably also TSEC, though the TRM isn't > clear about what power partition that's in (probably DISB because it's > used primary for HDMI, which is in DISB as well). I'd expect it would go away since the reset code in the driver would=20 activate then. >=20 > Thierry