From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Date: Tue, 01 Feb 2011 15:14:18 +0000 Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare Message-Id: <20110201151418.GN31216@n2100.arm.linux.org.uk> List-Id: References: <201102011711.31258.jeremy.kerr@canonical.com> <20110201105449.GY1147@pengutronix.de> <20110201140024.GZ1147@pengutronix.de> In-Reply-To: <20110201140024.GZ1147@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable To: linux-arm-kernel@lists.infradead.org On Tue, Feb 01, 2011 at 03:00:24PM +0100, Uwe Kleine-K=F6nig wrote: > On Tue, Feb 01, 2011 at 10:05:56PM +0900, Jassi Brar wrote: > > 2011/2/1 Uwe Kleine-K=F6nig : > >=20 > > ..... > >=20 > > > Do you plan to handle the case that clk_enable is called while prepare > > > isn't completed (considering the special case "not called at all")? > > > Maybe BUG_ON(clk->ops->prepare && !clk->prepare_count)? > > Sounds better than the second option. > >=20 > > > Alternatively don't force the sleep in clk_prepare (e.g. by protecting > > > prepare_count by a spinlock (probably enable_lock)) and call clk_prep= are > > > before calling clk->ops->enable? > > That might result in a driver working on some platforms(those have > > atomic clk_prepare) > > and not on others(those have sleeping). > The first option has the same result. E.g. on some platforms > clk->ops->prepare might be NULL, on others it's not. If clk->ops->prepare is NULL, then clk_prepare() better return success as it should mean "no preparation necessary", not "someone didn't implement it so its an error". Calling clk->ops->enable() with a spinlock held will ensure that no one tries to make that method sleep, so if people want sleeping stuff they have to use the clk_prepare() stuff. It's a self-enforcing API which ensures that we don't get sleeping stuff inside clk_enable(). And with a check in clk_enable() for a preparation, it helps to ensure that drivers do call clk_prepare() before clk_enable() - though it can't guarantee it in every case.