Messages in this thread | | | Subject | Re: [RFC work-in-progress 0/7] of: platform: use early platform routines instead of OF_DECLARE | From | Sekhar Nori <> | Date | Tue, 24 Apr 2018 13:48:00 +0530 |
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On Tuesday 24 April 2018 12:56 PM, Bartosz Golaszewski wrote: > 2018-04-23 23:38 GMT+02:00 David Lechner <david@lechnology.com>: >> FYI: It looks like the CC for Stephen and Arnd was messed up, so I >> fixed. >> > > Thanks! > >> On 04/23/2018 01:38 PM, Bartosz Golaszewski wrote: >>> >>> From: Bartosz Golaszewski <bgolaszewski@baylibre.com> >>> >>> Hi David, Sekhar, >>> >>> since platform devices are generally considered more desirable than >>> CLK_OF_DECLARE, TIMER_OF_DECLARE etc. and we need to figure out how to >>> handle the clocks that need to be initialized early in the boot >>> process on DaVinci, I thought that I could give the early_platform >>> mechanism a try. >>> >>> This API is only used on one architecture (sh) but seems to work just >>> fine on ARM. It allows to register early platform drivers and then >>> probe them early in the boot process. So far only machine code is >>> supported but with a bit of hacking I was able to probe a DT device. >>> >>> This is a very dirty and far-from-upstream proof of concept that allows >>> to probe the (so far dummy) davinci timer platform device during the >>> call to init_time (from machine_desc). >>> >>> The idea is to have a special compatible fallback string: "earlydev" >>> that similarily to "syscon" would be added to device nodes that need >>> early probing. Then we'd call the of_early_platform_populate() >>> function that would find all compatible nodes and populate them >>> long before all the "normal" nodes. >> >> >> FWIW, "earlydev" sounds like a driver implementation detail, so not >> something that should be included in the device tree. We only need >> this because Linux needs a clocksource early on, but that doesn't >> mean that all device tree users need to do the same. >> >> I'm sure it makes things easier for a proof of concept though. :-) >> > > We already have "syscon" which too is more an implementation detail > than HW description. I should have probably Cc'ed Rob Herring. I'll do > it with a more polished version I should have today.
Yeah, we should check with DT maintainers here. Even if there is push back on this, I suppose we can make of_early_platform_populate() take a list of compatible strings whose DT nodes should be considered early platform devices?
>>> This would allow us to make the davinci timer a normal platform device >>> and possibly also probe the psc and pll drivers earlier than we do now. >>> >>> The early platform API even allows us to check if we're being probed >>> early in probe() so we can possibly probe the driver twice if needed: >>> only doing the critical stuff first and then completing the process >>> later. >>> >>> If you think this is a good idea, I would like to continue on that >>> and eventually make it an alternative to OF_DECLARE macros. >>> >>> For a quick conversion of the davinci timer to a platform driver >>> I image we'd need to use platform data lookup that would be passed >>> to of_early_platform_populate(). >> >> >> On the surface, it certainly sounds like a good idea to me. Do we have >> access to struct device of the platform device when using this early >> platform device? I remember when I was working on the clock drivers, I >> tried registering a platform device in the init_time callback but the >> kernel crashed because kobj stuff was not initialized yet. I'm guessing >> that the early platform device somehow works around this. >> > > Yes, it seems we do. I was getting kobj stack dumps too when trying to > register a device using just platform_device_register() and it went > away as soon as I switched to early platform.
I agree, it sounds like a good idea to use for clock and timer devices. Thanks for looking into this. Looking forward to the more polished version.
Thanks, Sekhar
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