On Thu, 02 Apr 2015, Jassi Brar wrote: > On Wed, Apr 1, 2015 at 7:12 AM, Michael Turquette <mturquette@xxxxxxxxxx> wrote: > > Quoting Jassi Brar (2015-03-02 02:28:44) > >> On 2 March 2015 at 15:48, Lee Jones <lee.jones@xxxxxxxxxx> wrote: > >> > On Mon, 02 Mar 2015, Jassi Brar wrote: > >> > > >> >> On Mon, Mar 2, 2015 at 2:06 PM, Lee Jones <lee.jones@xxxxxxxxxx> wrote: > >> >> > On Sat, 28 Feb 2015, Jassi Brar wrote: > >> >> > > >> >> >> On 28 February 2015 at 02:44, Lee Jones <lee.jones@xxxxxxxxxx> wrote: > >> >> >> > Lots of platforms contain clocks which if turned off would prove fatal. > >> >> >> > The only way to recover from these catastrophic failures is to restart > >> >> >> > the board(s). Now, when a clock is registered with the framework it is > >> >> >> > compared against a list of provided always-on clock names which must be > >> >> >> > kept ungated. If it matches, we enable the existing CLK_IGNORE_UNUSED > >> >> >> > flag, which will prevent the common clk framework from attempting to > >> >> >> > gate it during the clk_disable_unused() procedure. > >> >> >> > > >> >> >> If a clock is critical on a certain board, it could be got+enabled > >> >> >> during early boot so there is always a user. > >> >> > > >> >> > I tried this. There was push-back from the DT maintainers. > >> >> > > >> >> > http://lists.infradead.org/pipermail/linux-arm-kernel/2015-February/324417.html > >> >> > > >> >> Thanks, I wasn't aware of the history. > >> >> > >> >> >> To be able to do that from DT, maybe add a new, say, CLK_ALWAYS_ON > >> >> >> flag could be made to initialize the clock with one phantom user > >> >> >> already. Or just reuse the CLK_IGNORE_UNUSED? > >> >> > > >> >> > How is that different to what this set is doing? > >> >> > > >> >> The phantom user - that's there but none can see it. > >> >> > >> >> How about? > >> >> > >> >> + of_property_for_each_string(np, "clock-always-on", prop, clkname) { > >> >> + clk = __clk_lookup(clkname); > >> >> + if (!clk) > >> >> + continue; > >> >> + > >> >> + clk->core->enable_count = 1; > >> >> + clk->core->prepare_count = 1; > >> >> + } > >> > > >> > This is only fractionally different from the current implementation. > >> > > >> > I believe the current way it slightly nicer, as we don't have to fake > >> > the user count. > >> > > >> Well... the user is indeed there, isn't it? It's just not known to > >> Linux. So 'fake' isn't most applicable here. > >> Otherwise you might have to stub out some existing and future > >> functions for CLK_IGNORE_UNUSED. And how do we explain to userspace > >> which would see power drawn but no user of the clock? > > > > Jassi, > > > > This is broken. What if the parent of this clock has > > {enable,prepare}_count of zero? The way we propagate these refcounts up > > the tree would fall over. > > > Yeah it needs to be done at higher level, > - clk->core->enable_count = 1; > - clk->core->prepare_count = 1; > + clk_prepare_enable(clk); FYI: https://lkml.org/lkml/2015/4/1/267 -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
