Re: [PATCH 1/4] ARM: OMAP2+: omap_hwmod: Introduce ti,no-init dt property

[Dave Gerlach <d-gerlach@ti.com>]

On 03/05/2015 12:49 PM, Tony Lindgren wrote:
> * Paul Walmsley <paul@pwsan.com> [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, 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.

Regards,
Dave

> So maybe the comments in the $subject patch are incorrect for that?
> 
> What we really should have is also status = "incomplete" where the
> dev entry gets created, but the driver never probes. This would be for
> devices that are still there within the SoC, but not pinned out for
> the board in question.
> 
> We still may need also ti,no-init too for devices that we don't want
> hwmod to do anything with, for example in secure mode if some blocks
> are not available to Linux at all. I believe that's what's going on with
> n900 crypto accelerators for example.
> 
> Regards,
> 
> Tony
>