Messages in this thread | | | Date | Tue, 3 Mar 2015 14:23:11 +0000 | From | Mark Brown <> | Subject | Re: [PATCH] regulator: core: Fix enable GPIO reference counting |
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On Mon, Mar 02, 2015 at 01:13:56PM -0800, Doug Anderson wrote: > On Mon, Mar 2, 2015 at 10:47 AM, Mark Brown <broonie@kernel.org> wrote:
> > Looking at the code it seems that you're adding checks to skip calls in > > the standard enable and disable paths but not touching other paths, > > based on this patch by itself I can't tell if this is a good idea or > > not. It certainly doesn't feel robust - if we're missing reference > > counting skipping operations seems likely to lead to other bugs popping > > up elsewhere when the other user that isn't doing a disable currently > > decides to start doing so.
> I guess it depends on whether _regulator_do_enable() on an > already-enabled rdev is supposed to be a noop or not. My assumption > was that it was supposed to be a noop with reference counting handled > by _regulator_enable().
Yes, that's the point.
> My assumption is that regulator drivers themselves shouldn't do > reference counting. That is: if you call > rdev->desc->ops->enable(rdev) twice you should not have to call > rdev->desc->ops->disable(rdev) twice to disable. Right? That means > my fix is making the "ena_pin" symmetric to how normal regulator > drivers work.
> The refcounting being skipped by my patch is refcounting that's used > only when the same GPIO is shared by more than one regulator. That > is, if "vcc_a" uses GPIO1 and "vcc_b" also uses "GPIO1" we need > refcounting. GPIO1 will be in the "on" state if either vcc_a or vcc_b > is on. The problem came in because _regulator_do_enable() was > incrementing the shared refcount every time it was called even if the > specific regulator was already on.
This is all analysis which should have been in the changelog... possibly not quite so verbosely but it should be there.
> Anyway, I looked at Javier's patch and it's also fine / reasonable. > ...and in fact I would argue that possibly we could take both patches. > Javier's patch eliminates the one known place where > _regulator_do_enable() is called for an already-enabled regulator and > my patch means that if someone else adds a new call we won't end up > back in this same subtle bug. I'm happy to update the CL desc to make > it more obvious if you'd like.
Yes, the changelog definitely needs to be *much* clearer. Especially for things like locking and reference counting the changelog needs to explain what the fix is and why it's safe, without that working it is a lot harder to do a review as the reviewer needs to go back and check that everything has been thought through properly. [unhandled content-type:application/pgp-signature] | |