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Looking into this issue, before this commit was applied, >>>> if any of the Tegra power-domains were in 'on' state when the kernel >>>> booted, they were being turned off by the genpd core before any driver >>>> had chance to request them. This was purely by luck and a consequence of >>>> the power-domains being turned off earlier during boot. After this >>>> commit was applied, any power-domains in the 'on' state are kept on for >>>> longer during boot and therefore, may never transitioned to the off >>>> state before they are requested/used. The hang on the Tegra210 Jetson >>>> TX1 is caused because devices in some power-domains are accessed without >>>> the power-domain being turned off and on, indicating that the >>>> power-domain is not in a completely on state. >>>> >>>> From reviewing the Tegra PMC driver code, if a power-domain is in the >>>> 'on' state there is no guarantee that all the necessary clocks >>>> associated with the power-domain are on and even if they are they would >>>> not have been requested via the clock framework and so could be turned >>>> off later. Some power-domains also have a 'clamping' register that needs >>>> to be configured as well. In short, if a power-domain is already 'on' it >>>> is difficult to know if it has been configured correctly. Given that the >>>> power-domains happened to be switched off during boot previously, to >>>> ensure that they are in a good known state on boot, fix this by >>>> switching off any power-domains that are on initially when registering >>>> the power-domains with the genpd framework. >>>> >>>> Note that commit 05cfb988a4d0 ("soc/tegra: pmc: Initialise resets >>>> associated with a power partition") updated the >>>> tegra_powergate_of_get_resets() function to pass the 'off' to ensure >>>> that the resets for the power-domain are in the correct state on boot. >>>> However, now that we may power off a domain on boot, if it is on, it is >>>> better to move this logic into the tegra_powergate_add() function so >>>> that there is a single place where we are handling the initial state of >>>> the power-domain. >>>> >>>> Fixes: a38045121bf4 ("soc/tegra: pmc: Add generic PM domain support") >>>> Signed-off-by: Jon Hunter >>> >>> Thanks for looking into this! >>> >>> I have picked this up via my pmdomain tree and applied it as a fix >>> with a stable tag. Please let me know if you prefer to take this via >>> your soc tree instead. >>> >>> That said, I guess we have some use-cases on Tegra where it actually >>> would make sense to allow powered-on PM-domains to stay on during >>> boot. Although, at this point, it seems better to deal with those on a >>> case by case basis, as improvements on top. >> >> We're actually running into one of these cases right now. This happens >> for display hardware where we have simple-framebuffer device tree nodes >> that are meant to allow a seamless transition from the firmware's early >> framebuffer to the Linux framebuffer. But since Jon's patch disables all >> of the power domains, the seamless transition no longer works. >> >> I suppose we could argue that seamless display is less important than >> systems booting, so I'm inclined to say we want to keep this patch to >> fix the earlier regression and then apply a fix on top to address the >> issue with the early display. >> >> Do you have any thoughts on how to deal with specific power domains that >> should remain powered on during boot? Ideally it would be something >> standard, but worst case we can also special-case in the Tegra PMC >> driver. > > Does it work to leave that particular PM domain for the display powered-on? > > Genpd should deal with this then, by simply leaving the PM domain on, > until the consumers of it have been probed. I need to check that but that could be a good idea. Thanks Jon -- nvpublic