From mboxrd@z Thu Jan 1 00:00:00 1970 From: jamie@jamieiles.com (Jamie Iles) Date: Thu, 12 Jan 2012 18:37:28 +0000 Subject: Clock API and "maximum rate" In-Reply-To: References: <20120111165844.GL3226@page> <20120112141128.GK1068@n2100.arm.linux.org.uk> Message-ID: <20120112183728.GA13991@page> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Jan 12, 2012 at 08:48:11AM -0600, Matt Sealey wrote: > On Thu, Jan 12, 2012 at 8:11 AM, Russell King - ARM Linux > wrote: > > On Thu, Jan 12, 2012 at 07:49:35AM -0600, Matt Sealey wrote: > >> On Wed, Jan 11, 2012 at 10:58 AM, Jamie Iles wrote: > >> > Hi Matt, > >> > > >> > On Wed, Jan 11, 2012 at 10:30:15AM -0600, Matt Sealey wrote: > >> >> Just a curious question, is there any safe way in the current API or > >> >> even by peeking a little behind the scenes to find out what the > >> >> maximum clock rate would be for a given named clock or struct clk? > >> > > >> > How about: > >> > > >> > ? ? ? ?long max = clk_round_rate(clk, ~0LU); > >> > > >> > clk_round_rate() is one of the optional API calls though. > >> > >> Luckily implemented in this case :) Seems to do the trick, thanks. > > > > If it's not implemented, but there is an implemented clk_set_rate(), feel > > free to complain at whoever created the implementation. > > > > If there's a clk_set_rate() implementation, then there's _already_ an > > implementation of clk_round_rate() internally doing the rounding for the > > set_rate function, so there's really no excuse not to expose that via > > clk_round_rate(). > > > > clk_round_rate() is supposed to tell you what you end up with if you > > ask clk_set_rate() to set the exact same value you passed in - but > > clk_round_rate() won't modify the hardware. > > > > So, clk_round_rate/clk_set_rate really should be thought of being > > implemented as this: > > > > long clk_round_rate(struct clk *clk, unsigned long rate) > > { > > ? ? ? ?return __clk_round_rate(clk, rate); > > } > > > > int clk_set_rate(struct clk *clk, unsigned long rate) > > { > > ? ? ? ?long rate = __clk_round_rate(clk, rate); > > > > ? ? ? ?if (rate < 0) > > ? ? ? ? ? ? ? ?return rate; > > > > ? ? ? ?return __clk_set_rate(clk, rate); > > } > > Right. On i.MX it seems not to round first, but to assume you passed a > rounded rate? I assume the upper level clk API does the above, so the > low level doesn't have to? Well each platform implements the whole clock API itself at the moment so I guess the higher layer is in plat-mxc? If so then something like the (untested) patch below may do the trick. clk_round_rate() for this platform returns 0 when it fails though and that's not right from the API: /** * clk_round_rate - adjust a rate to the exact rate a clock can provide * @clk: clock source * @rate: desired clock rate in Hz * * Returns rounded clock rate in Hz, or negative errno. */ Jamie 8<--- diff --git a/arch/arm/plat-mxc/clock.c b/arch/arm/plat-mxc/clock.c index 2ed3ab1..64f679b 100644 --- a/arch/arm/plat-mxc/clock.c +++ b/arch/arm/plat-mxc/clock.c @@ -134,7 +134,7 @@ EXPORT_SYMBOL(clk_get_rate); long clk_round_rate(struct clk *clk, unsigned long rate) { if (clk == NULL || IS_ERR(clk) || !clk->round_rate) - return 0; + return -EOPNOTSUPP; return clk->round_rate(clk, rate); } @@ -146,12 +146,17 @@ EXPORT_SYMBOL(clk_round_rate); int clk_set_rate(struct clk *clk, unsigned long rate) { int ret = -EINVAL; + long rounded_rate; if (clk == NULL || IS_ERR(clk) || clk->set_rate == NULL || rate == 0) return ret; + rounded_rate = clock_round_rate(clk, rate); + if (rounded_rate < 0) + return rounded_rate; + mutex_lock(&clocks_mutex); - ret = clk->set_rate(clk, rate); + ret = clk->set_rate(clk, rounded_rate); mutex_unlock(&clocks_mutex); return ret;