Re: [PATCH V6 03/10] PM / Domains: Add function to remove a pm-domain

Jon Hunter
2016-02-29T10:14:47Z

On 29/02/16 07:15, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Fri, Feb 26, 2016 at 03:48:37PM +0000, Jon Hunter wrote:
>> The genpd framework allows users to add power-domains via the
>> pm_genpd_init() function, however, there is no corresponding function
>> to remove a power-domain. For most devices this may be fine as the power
>> domains are never removed, however, for devices that wish to populate
>> the power-domains from within a driver, having the ability to remove a
>> power domain if the probing of the device fails or the driver is unloaded
>> is necessary. Therefore, add a function to remove a power-domain. Please
>> note that the power domain can only be removed if there are no devices
>> using the power-domain and it is not linked to another domain.
>
> So I guess this introduces a problem not uncommon to other types of
> resources. If you remove the driver, even if you fail ->remove() the
> module may still go away along with any code associated with it. So
> even if the PM domains can't be removed, you can't prevent the module
> from going away. That could be somewhat mitigated if we were holding a
> module reference count, because then the only way to unload the driver
> would be via sysfs (we could prevent that too, which might be the best
> way to do this today).
>
> There is work underway to solve this generically, Rafael was working on
> this, so I'm not sure we need to add additional infrastructure to the PM
> domain code as part of this series. But we may want to mark the Tegra
> PMC driver as .suppress_bind_attrs = true, to make sure it can't be
> removed.

I see what you are saying. It nearly seemed to me that I should use
BUG_ON() if we fail to remove a genpd in the PMC driver, however, I know
that using BUG_ON should be avoided. I will add the suppress_bind_attrs
= true for the PMC driver as that does make sense for now.

Jon