From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Turquette Subject: Re: [PATCH v7 3/5] clk: Supply the critical clock {init, enable, disable} framework Date: Wed, 29 Jul 2015 18:19:32 -0700 Message-ID: <20150730011932.642.85168@quantum> References: <1437570255-21049-1-git-send-email-lee.jones@linaro.org> <1437570255-21049-4-git-send-email-lee.jones@linaro.org> <20150727072549.GP2564@lukather> <20150727085338.GW3436@x1> <20150728114022.GW2564@lukather> <20150728130055.GV14943@x1> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20150728130055.GV14943@x1> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Lee Jones , Maxime Ripard Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-F5mvAk5X5gdBDgjK7y7TUQ@public.gmane.org, sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org, s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org List-Id: devicetree@vger.kernel.org Quoting Lee Jones (2015-07-28 06:00:55) > On Tue, 28 Jul 2015, Maxime Ripard wrote: >=20 > > On Mon, Jul 27, 2015 at 09:53:38AM +0100, Lee Jones wrote: > > > On Mon, 27 Jul 2015, Maxime Ripard wrote: > > >=20 > > > > On Wed, Jul 22, 2015 at 02:04:13PM +0100, Lee Jones wrote: > > > > > These new API calls will firstly provide a mechanisms to tag = a clock as > > > > > critical and secondly allow any knowledgeable driver to (un)g= ate clocks, > > > > > even if they are marked as critical. > > > > >=20 > > > > > Suggested-by: Maxime Ripard > > > > > Signed-off-by: Lee Jones > > > > > --- > > > > > drivers/clk/clk.c | 45 ++++++++++++++++++++++++++= ++++++++++++++++++ > > > > > include/linux/clk-provider.h | 2 ++ > > > > > include/linux/clk.h | 30 ++++++++++++++++++++++++++= +++ > > > > > 3 files changed, 77 insertions(+) > > > > >=20 > > > > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > > > > > index 61c3fc5..486b1da 100644 > > > > > --- a/drivers/clk/clk.c > > > > > +++ b/drivers/clk/clk.c > > > > > @@ -46,6 +46,21 @@ static struct clk_core *clk_core_lookup(co= nst char *name); > > > > > =20 > > > > > /*** private data structures ***/ > > > > > =20 > > > > > +/** > > > > > + * struct critical - Provides 'play' over critical clocks.= A clock can be > > > > > + * marked as critical, meaning that it s= hould not be > > > > > + * disabled. However, if a driver which= is aware of the > > > > > + * critical behaviour wants to control i= t, it can do so > > > > > + * using clk_enable_critical() and clk_d= isable_critical(). > > > > > + * > > > > > + * @enabled Is clock critical? Once set, doesn't change > > > > > + * @leave_on Self explanatory. Can be disabled by knowled= geable drivers > > > > > + */ > > > > > +struct critical { > > > > > + bool enabled; > > > > > + bool leave_on; > > > > > +}; > > > > > + > > > > > struct clk_core { > > > > > const char *name; > > > > > const struct clk_ops *ops; > > > > > @@ -75,6 +90,7 @@ struct clk_core { > > > > > struct dentry *dentry; > > > > > #endif > > > > > struct kref ref; > > > > > + struct critical critical; > > > > > }; > > > > > =20 > > > > > struct clk { > > > > > @@ -995,6 +1011,10 @@ static void clk_core_disable(struct clk= _core *clk) > > > > > if (WARN_ON(clk->enable_count =3D=3D 0)) > > > > > return; > > > > > =20 > > > > > + /* Refuse to turn off a critical clock */ > > > > > + if (clk->enable_count =3D=3D 1 && clk->critical.leave= _on) > > > > > + return; > > > > > + > > > >=20 > > > > I think it should be handled by a separate counting. Otherwise,= if you > > > > have two users that marked the clock as critical, and then one = of them > > > > disable it... > > > >=20 > > > > > if (--clk->enable_count > 0) > > > > > return; > > > > > =20 > > > > > @@ -1037,6 +1057,13 @@ void clk_disable(struct clk *clk) > > > > > } > > > > > EXPORT_SYMBOL_GPL(clk_disable); > > > > > =20 > > > > > +void clk_disable_critical(struct clk *clk) > > > > > +{ > > > > > + clk->core->critical.leave_on =3D false; > > > >=20 > > > > .. you just lost the fact that it was critical in the first pla= ce. > > >=20 > > > I thought about both of these points, which is why I came up with= this > > > strategy. > > >=20 > > > Any device which uses the *_critical() API should a) have knowled= ge of > > > what happens when a particular critical clock is gated and b) hav= e > > > thought about the consequences. > >=20 > > Indeed. > >=20 > > > I don't think we can use reference counting, because we'd need as > > > many critical clock owners as there are critical clocks. > >=20 > > Which we can have if we replace the call to clk_prepare_enable you = add > > in your fourth patch in __set_critical_clocks. >=20 > What should it be replaced with? >=20 > > > Cast your mind back to the reasons for this critical clock API. = One > > > of the most important intentions of this API is the requirement > > > mitigation for each of the critical clocks to have an owner > > > (driver). > > >=20 > > > With regards to your second point, that's what 'critical.enabled' > > > is for. Take a look at clk_enable_critical(). > >=20 > > I don't think this addresses the issue, if you just throw more > > customers at it, the issue remain with your implementation. > >=20 > > If you have three customers that used the critical API, and if on o= f > > these calls clk_disable_critical, you're losing leave_on. >=20 > That's the idea. See my point above, the one you replied "Indeed" > to. So when a driver uses clk_disable_critical() it's saying, "I kno= w > why this clock is a critical clock, and I know that nothing terrible > will happen if I disable it, as I have that covered". So then if it'= s > not the last user to call clk_disable(), the last one out the door > will be allowed to finally gate the clock, regardless whether it's > critical aware or not. >=20 > Then, when we come to enable the clock again, the critical aware user > then re-marks the clock as leave_on, so not critical un-aware user ca= n > take the final reference and disable the clock. >=20 > > Which means that if there's one of the two users left that calls > > clk_disable on it, the clock will actually be disabled, which is > > clearly not what we want to do, as we have still a user that want t= he > > clock to be enabled. >=20 > That's not what happens (at least it shouldn't if I've coded it up > right). The API _still_ requires all of the users to give-up their > reference. >=20 > > It would be much more robust to have another count for the critical > > stuff, initialised to one by the __set_critical_clocks function. >=20 > If I understand you correctly, we already have a count. We use the > original reference count. No need for one of our own. >=20 > Using your RAM Clock (Clock 4) as an example > -------------------------------------------- >=20 > Early start-up: > Clock 4 is marked as critical and a reference is taken (ref =3D=3D = 1) >=20 > Driver probe: > SPI enables Clock 4 (ref =3D=3D 2) > I2C enables Clock 4 (ref =3D=3D 3) >=20 > Suspend (without RAM driver's permission): > SPI disables Clock 4 (ref =3D=3D 2) > I2C disables Clock 4 (ref =3D=3D 1) > /* > * Clock won't be gated because: > * .leave_on is True - can't dec final reference I am clearly missing the point. The clock won't be gated because the enable_count is still 1! What does .leave_on do here? > */ >=20 > Suspend (with RAM driver's permission): > /* Order is unimportant */ > SPI disables Clock 4 (ref =3D=3D 2) > RAM disables Clock 4 (ref =3D=3D 1) /* Won't turn off here (ref > 0= ) > I2C disables Clock 4 (ref =3D=3D 0) /* (.leave_on =3D=3D False) las= t ref can be taken */ > /* > * Clock will be gated because: > * .leave_on is False, so (ref =3D=3D 0) Again, .leave_on does nothing new here. We gate the clock because the reference count is 0. > */ >=20 > Resume: > /* Order is unimportant */ > SPI enables Clock 4 (ref =3D=3D 1) > RAM enables Clock 4 and re-enables .leave_on (ref =3D=3D 2) > I2C enables Clock 4 (ref =3D=3D 3) Same again. As soon as RAM calls clk_enable_critical the ref count goes up. .leave_on does nothing as far as I can tell. The all works because of the reference counting, which already exists before this patch series. Regards, Mike >=20 > Hopefully that clears things up. >=20 > Please tell me if the code doesn't reflect this strategy, or if you > can see anything wrong with how it operates. >=20 > --=20 > Lee Jones > Linaro STMicroelectronics Landing Team Lead > Linaro.org =E2=94=82 Open source software for ARM SoCs > Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe devicetree" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html