Messages in this thread | | | From | Bartosz Golaszewski <> | Date | Tue, 24 Apr 2018 09:26:37 +0200 | Subject | Re: [RFC work-in-progress 0/7] of: platform: use early platform routines instead of OF_DECLARE |
| |
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.
>> >> 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.
Best regards, Bartosz Golaszewski
| |