From mboxrd@z Thu Jan 1 00:00:00 1970 From: Saravana Kannan Date: Tue, 01 Feb 2011 20:21:45 +0000 Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare Message-Id: <4D486B59.6010106@codeaurora.org> List-Id: References: <201102011711.31258.jeremy.kerr@canonical.com> <20110201105449.GY1147@pengutronix.de> <20110201131512.GH31216@n2100.arm.linux.org.uk> <20110201141837.GA1147@pengutronix.de> <20110201143932.GK31216@n2100.arm.linux.org.uk> <20110201151846.GD1147@pengutronix.de> <20110201152458.GP31216@n2100.arm.linux.org.uk> <20110201155344.GF1147@pengutronix.de> <20110201170637.GR31216@n2100.arm.linux.org.uk> <20110201193201.GH1147@pengutronix.de> <20110201195604.GS31216@n2100.arm.linux.org.uk> In-Reply-To: <20110201195604.GS31216@n2100.arm.linux.org.uk> 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 02/01/2011 11:56 AM, Russell King - ARM Linux wrote: > On Tue, Feb 01, 2011 at 08:32:01PM +0100, Uwe Kleine-K=F6nig wrote: >> On Tue, Feb 01, 2011 at 05:06:37PM +0000, Russell King - ARM Linux wrote: >>> So? You're not _supposed_ to call it from any atomic context ever. >> >> My motivation for a more complicated clk_prepare was to make clk_prepare >> atomic when that's possible (i.e. when the clk is already prepared) and >> call it before the enable callback in clk_enable. Then everything >> behaves nicely even if clk_enable is called from atomic context provided >> that the clock was prepared before (or doesn't need to). > > You really don't get the point of clk_prepare() do you. I'm not > going to bother trying to educate you anymore. > > Hopefully someone with more patience can give you the necessary > teaching to make you understand. Uwe, If the driver is calling clk_prepare() right next to clk_enable()=20 knowing it's been already prepared and will hence be "atomic" (this is=20 actually not true), then by your description, it's pointless to call=20 clk_prepare(). If you want the driver to call clk_prepare() in atomic context because=20 it will be atomic in most cases -- well, that's wrong. It's either=20 atomic or is NOT atomic. There is no in between. If a call is NOT=20 atomic, it can't be called in atomic context. Long story short, if you=20 expect clk_prepare() to be atomic under any circumstance, it beats the=20 point of introducing clk_prepare(). Hope I helped. -Saravana --=20 Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.