From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 To: Geert Uytterhoeven , From: Michael Turquette In-Reply-To: Cc: "linux-kernel@vger.kernel.org" , "linux-clk" , "Stephen Boyd" , "Lee Jones" , "Maxime Ripard" , "Sascha Hauer" , "Sekhar Nori" , "Kevin Hilman" , "Santosh Shilimkar" , "Tony Lindgren" , "linux-omap@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "Linux-sh list" , "Linux PM list" References: <1438974570-20812-1-git-send-email-mturquette@baylibre.com> <1438974570-20812-3-git-send-email-mturquette@baylibre.com> Message-ID: <20151020124000.20687.60752@quantum> Subject: Re: [PATCH RFC RFT 2/3] clk: clk_put WARNs if user has not disabled clk Date: Tue, 20 Oct 2015 05:40:00 -0700 List-ID: Hi Geert, Quoting Geert Uytterhoeven (2015-09-30 08:38:46) > Hi Mike, > = > On Fri, Aug 7, 2015 at 9:09 PM, Michael Turquette > wrote: > > From the clk_put kerneldoc in include/linux/clk.h: > > > > """ > > Note: drivers must ensure that all clk_enable calls made on this clock > > source are balanced by clk_disable calls prior to calling this function. > > """ > > > > The common clock framework implementation of the clk.h api has per-user > > reference counts for calls to clk_prepare and clk_disable. As such it > > can enforce the requirement to properly call clk_disable and > > clk_unprepare before calling clk_put. > > > > Because this requirement is probably violated in many places, this patch > > starts with a simple warning. Once offending code has been fixed this > > check could additionally release the reference counts automatically. > > > > Signed-off-by: Michael Turquette > > --- > > drivers/clk/clk.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > > index 72feee9..6ec0f77 100644 > > --- a/drivers/clk/clk.c > > +++ b/drivers/clk/clk.c > > @@ -2764,6 +2764,14 @@ void __clk_put(struct clk *clk) > > clk->max_rate < clk->core->req_rate) > > clk_core_set_rate_nolock(clk->core, clk->core->req_rate= ); > > > > + /* > > + * before calling clk_put, all calls to clk_prepare and clk_ena= ble from > > + * a given user must be balanced with calls to clk_disable and > > + * clk_unprepare by that same user > > + */ > > + WARN_ON(clk->prepare_count); > > + WARN_ON(clk->enable_count); > = > These two WARN_ON()s are triggered a lot when using a legacy clock domain, > and CONFIG_PM=3Dn. Indeed, without Runtime PM, the idea is that the modul= e clocks > get enabled unconditionally, which violates the assumptions above. > = > Cfr. the CONFIG_PM=3Dn version of pm_clk_notify() in > drivers/base/power/clock_ops.c, which calls enable_clock(): > = > /** > * enable_clock - Enable a device clock. > * @dev: Device whose clock is to be enabled. > * @con_id: Connection ID of the clock. > */ > static void enable_clock(struct device *dev, const char *con_id) > { > struct clk *clk; > = > clk =3D clk_get(dev, con_id); > if (!IS_ERR(clk)) { > clk_prepare_enable(clk); > clk_put(clk); This is a violation of the clkdev api as defined in include/linux/clk.h: /** * clk_put|------ "free" the clock source * @clk: clock source * * Note: drivers must ensure that all clk_enable calls made on this * clock source are balanced by clk_disable calls prior to calling * this function. So the WARN is doing its job and letting us know about incorrect use of the API. > dev_info(dev, "Runtime PM disabled, clock forced on.\= n"); > } > } > = > I think this affects shmobile, keystone, davinci, omap1, and legacy sh. Why not keep the reference to the struct clk after get'ing it the first time? > = > Sorry for not noticing before, we usually build with CONFIG_PM=3Dy. > One more reason for making CONFIG_PM=3Dy mandatory on SoCs with clock dom= ains? I don't know about that, but it seems like a reason to fix the clkdev usage in the clock domain code. What do you think? Regards, Mike > = > Gr{oetje,eeting}s, > = > Geert > = > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m6= 8k.org > = > In personal conversations with technical people, I call myself a hacker. = But > when I'm talking to journalists I just say "programmer" or something like= that. > -- Linus Torvalds