* Dave Gerlach <d-gerlach@xxxxxx> [150306 09:28]: > On 03/05/2015 06:41 PM, Tony Lindgren wrote: > > * Tony Lindgren <tony@xxxxxxxxxxx> [150305 12:24]: > >> * Dave Gerlach <d-gerlach@xxxxxx> [150305 11:53]: > >>> On 03/05/2015 12:49 PM, Tony Lindgren wrote: > >>>> * Paul Walmsley <paul@xxxxxxxxx> [150305 10:16]: > >>>>> On Thu, 5 Mar 2015, Dave Gerlach wrote: > >>>>> > >>>>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization. > >>>>>> Even if a dt node is marked as disabled, hwmod still at least enables > >>>>>> the hwmod and programs the sysconfig before attempting to idle it at > >>>>>> boot. If an IP has been disabled by the hardware configuration on a > >>>>>> platform, this will cause a hang due to writing to inactive registers. > >>>>>> This property prevents that from happening by marking the hwmod as > >>>>>> _HWMOD_STATE_DISABLED during init. > >>>>> > >>>>> I'm kind of wondering if hwmod should even touch a device if it's marked > >>>>> as disabled in the DT. Tony, what do you think? > >>>> > >>>> Well nothing happens if a device is status = "disabled". No dev entry > >>>> gets created for it at all and hwmod won't have any data for the device > >>>> populated. The only way hwmod code could see that device if the device > >>>> gets it's data from the legacy omap_hwmod_*_data.c instead of DT. > >>>> > >>> > >>> We still need this for the sysconfig programming, correct? hwmod programs that > >>> regardless of dt status and then idles the IP, > >> > >> Well hwmod does not even know about the IP IO addresses if it's marked > >> with status = "disabled".. Which IP are you having problems with? > >> > >>> which is why I needed the ti,no-init for the epos evm. It isn't just a > >>> matter of we shouldnt write to it because we don't want to use it; we > >>> can't write to it because the module is held off so it causes an > >>> external abort if we do. > >> > >> Well hard to say not knowing which module this is.. Pretty much all > >> the modules have drivers and the driver just does pm_runtime_get() > >> on it? > > > > Heh OK this thread is about the RTC driver, so I assume that's the > > problem :) So if you set the rtc to status = "disabled" how can the > > hwmod code do anything as AFAIK it won't even get the rtc IO address? > > > > Or am I missing something here? > > Perhaps I am mistaken, but from what I understand, all hwmods have _init and > _setup called on them, and all hwmods read the IO address regardless of DT > status at this point with _init_mpu_rt_base. In _setup, _setup_reset gets called > which calls _enable for the hwmod, and this calls both _enable_sysc and > _update_sysc_cache which touch the sysconfig register of the IP. Oh OK, I think you're right. I was thinking of omap_device_build_from_dt(), sorry. Looks like the hwmod IO address data does get populated even for status = "disabled" although the dev entry won't get created and omap_device_build_from_dt() never gets called. > Normally this is fine regardless of whether or not we are using an IP because > the module will wake up for a moment, have it's sysc programmed, and then be put > back to sleep later, potentially never to be woken again if we bind no driver > for it, which is fine for 99% of cases. In the case of am43x epos evm, you can > take the same piece of silicon that will boot happily on the gp evm with the rtc > hwmod in place and it will hang during boot on the epos evm because the board > uses a pin to hold the RTC IP in reset. There is no way to detect this in > software, the module can be turned on as normal using the clk_ctrl, but if you > touch any of the IP registers you get an abort. OK sounds like some dts property is needed to signal this. > So we need to prevent this from happening but of course we can't selectively > choose when the rtc hwmod gets added based on which board we are using so it > seemed a DT flag was appropriate to indicate that we do not want to init the rtc > IP at all only on this board. > > Without this flag in place but with the rtc hwmod added, the am43x-epos-evm > fails booting with an imprecise abort. OK thanks for explaining it. I'm fine with this patch, Paul may have other issues. The other option would be to use status = "disabled" to not touch the device at all like Paul suggested. I wonder if that's going to break PM on some devices though.. Regards, Tony -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
