| Message ID | 20170214210114.5846-1-dianders@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hello Doug, On Tue, Feb 14, 2017 at 6:01 PM, Douglas Anderson <dianders@chromium.org> wrote: > The PMU Cortex M0 on rk3399 is intended to be used for things like > DDRFreq transitions, suspend/resume, and other things that are the > purview of ARM Trusted Firmware and not the kernel. As such, the > kernel shouldn't be messing with the clocks. Add CLK_IGNORE_UNUSED to > these clocks. > Isn't CLK_IS_CRITICAL a more suitable flag for this case? Best regards, Javier
Hi, On Wed, Feb 15, 2017 at 7:27 AM, Javier Martinez Canillas <javier@dowhile0.org> wrote: > Hello Doug, > > On Tue, Feb 14, 2017 at 6:01 PM, Douglas Anderson <dianders@chromium.org> wrote: >> The PMU Cortex M0 on rk3399 is intended to be used for things like >> DDRFreq transitions, suspend/resume, and other things that are the >> purview of ARM Trusted Firmware and not the kernel. As such, the >> kernel shouldn't be messing with the clocks. Add CLK_IGNORE_UNUSED to >> these clocks. >> > > Isn't CLK_IS_CRITICAL a more suitable flag for this case? As I understand it (AKA please correct me if I'm wrong)... Usually CLK_IS_CRITICAL is more suitable than CLK_IGNORE_UNUSED since lots of old code used CLK_IGNORE_UNUSED for critical clocks before CLK_IS_CRITICAL existed. ...but in this case, I don't think it is more suitable. CLK_IS_CRITICAL means that the kernel should be in charge of keeping this clock on at all times. The documentation I see says: #define CLK_IS_CRITICAL BIT(11) /* do not gate, ever */ In our case, as was so eloquently described in our private bug by our firmware engineer: Just tell the kernel to keep its grubby hands off my clocks completely AKA: this isn't a clock that the kernel should touch--it is entirely managed by the firmware. It's OK for the kernel to show it in the clock tree, but otherwise "hands off". -Doug
Am Mittwoch, 15. Februar 2017, 12:27:59 CET schrieb Javier Martinez Canillas: > Hello Doug, > > On Tue, Feb 14, 2017 at 6:01 PM, Douglas Anderson <dianders@chromium.org> wrote: > > The PMU Cortex M0 on rk3399 is intended to be used for things like > > DDRFreq transitions, suspend/resume, and other things that are the > > purview of ARM Trusted Firmware and not the kernel. As such, the > > kernel shouldn't be messing with the clocks. Add CLK_IGNORE_UNUSED to > > these clocks. > > Isn't CLK_IS_CRITICAL a more suitable flag for this case? From the patch description it looks like the clock is expected to be controlled from firmware in most cases as I guess the Cortex M0 will be used for that all the time now. And the clock is not expected to run all the time. So I'd think clk_ignore_unused is the correct one. The whole clock-subtree for these clocks also does not get affected by other clocks, as it is independendly coming from PLLs. Heiko
Hello Heiko and Doug, On Wed, Feb 15, 2017 at 2:01 PM, Heiko Stübner <heiko@sntech.de> wrote: > Am Mittwoch, 15. Februar 2017, 12:27:59 CET schrieb Javier Martinez Canillas: >> Hello Doug, >> >> On Tue, Feb 14, 2017 at 6:01 PM, Douglas Anderson <dianders@chromium.org> > wrote: >> > The PMU Cortex M0 on rk3399 is intended to be used for things like >> > DDRFreq transitions, suspend/resume, and other things that are the >> > purview of ARM Trusted Firmware and not the kernel. As such, the >> > kernel shouldn't be messing with the clocks. Add CLK_IGNORE_UNUSED to >> > these clocks. >> >> Isn't CLK_IS_CRITICAL a more suitable flag for this case? > > From the patch description it looks like the clock is expected to be > controlled from firmware in most cases as I guess the Cortex M0 will be used > for that all the time now. And the clock is not expected to run all the time. > > So I'd think clk_ignore_unused is the correct one. The whole clock-subtree for > these clocks also does not get affected by other clocks, as it is > independendly coming from PLLs. > > I see. Thanks a lot for your explanations. I just asked because CLK_IGNORE_UNUSED only prevents the clock to be disabled by clk_disable_unused() but still can be disabled if a driver explicitly looks it up and calls clk_disable() or if the clock is affected by other clocks. But I understand now that both scenarios are not possible. So yes, CLK_IGNORE_UNUSED is more suitable in this case. > Heiko Best regards, Javier
Am Dienstag, 14. Februar 2017, 13:01:14 CET schrieb Douglas Anderson: > The PMU Cortex M0 on rk3399 is intended to be used for things like > DDRFreq transitions, suspend/resume, and other things that are the > purview of ARM Trusted Firmware and not the kernel. As such, the > kernel shouldn't be messing with the clocks. Add CLK_IGNORE_UNUSED to > these clocks. > > Without this change, the following was observed on a Chromebook with a > rk3399 (using not-yet-upstream ARM Trusted Firmware code and > not-yet-upstream kernel code based on kernel-4.4): > > 1. We init the clock framework. > > 2. We start up "DDRFreq", which causes ATF to occasionally fire up the > M0 for transitions. Each time ATF fires up the M0 it will turn on > these clocks and each time it is done it will turn them off. > > 3. We finally get to the the part of the kernel that calls > clk_disable_unused() and we disables the clocks. > > You can see the race above. Basically everything is fine as long as > ARM Trusted Firmware isn't starting up the M0 at exactly the same time > that the kernel is disabling unused clocks. ...but if the race > happens then we go boom. > > Signed-off-by: Douglas Anderson <dianders@chromium.org> applied for 4.12 Thanks Heiko
diff --git a/drivers/clk/rockchip/clk-rk3399.c b/drivers/clk/rockchip/clk-rk3399.c index 73121b144634..fa3cbef08776 100644 --- a/drivers/clk/rockchip/clk-rk3399.c +++ b/drivers/clk/rockchip/clk-rk3399.c @@ -1477,10 +1477,10 @@ static struct rockchip_clk_branch rk3399_clk_pmu_branches[] __initdata = { GATE(PCLK_UART4_PMU, "pclk_uart4_pmu", "pclk_pmu_src", 0, RK3399_PMU_CLKGATE_CON(1), 14, GFLAGS), GATE(PCLK_WDT_M0_PMU, "pclk_wdt_m0_pmu", "pclk_pmu_src", 0, RK3399_PMU_CLKGATE_CON(1), 15, GFLAGS), - GATE(FCLK_CM0S_PMU, "fclk_cm0s_pmu", "fclk_cm0s_src_pmu", 0, RK3399_PMU_CLKGATE_CON(2), 0, GFLAGS), - GATE(SCLK_CM0S_PMU, "sclk_cm0s_pmu", "fclk_cm0s_src_pmu", 0, RK3399_PMU_CLKGATE_CON(2), 1, GFLAGS), - GATE(HCLK_CM0S_PMU, "hclk_cm0s_pmu", "fclk_cm0s_src_pmu", 0, RK3399_PMU_CLKGATE_CON(2), 2, GFLAGS), - GATE(DCLK_CM0S_PMU, "dclk_cm0s_pmu", "fclk_cm0s_src_pmu", 0, RK3399_PMU_CLKGATE_CON(2), 3, GFLAGS), + GATE(FCLK_CM0S_PMU, "fclk_cm0s_pmu", "fclk_cm0s_src_pmu", CLK_IGNORE_UNUSED, RK3399_PMU_CLKGATE_CON(2), 0, GFLAGS), + GATE(SCLK_CM0S_PMU, "sclk_cm0s_pmu", "fclk_cm0s_src_pmu", CLK_IGNORE_UNUSED, RK3399_PMU_CLKGATE_CON(2), 1, GFLAGS), + GATE(HCLK_CM0S_PMU, "hclk_cm0s_pmu", "fclk_cm0s_src_pmu", CLK_IGNORE_UNUSED, RK3399_PMU_CLKGATE_CON(2), 2, GFLAGS), + GATE(DCLK_CM0S_PMU, "dclk_cm0s_pmu", "fclk_cm0s_src_pmu", CLK_IGNORE_UNUSED, RK3399_PMU_CLKGATE_CON(2), 3, GFLAGS), GATE(HCLK_NOC_PMU, "hclk_noc_pmu", "fclk_cm0s_src_pmu", CLK_IGNORE_UNUSED, RK3399_PMU_CLKGATE_CON(2), 5, GFLAGS), };
The PMU Cortex M0 on rk3399 is intended to be used for things like DDRFreq transitions, suspend/resume, and other things that are the purview of ARM Trusted Firmware and not the kernel. As such, the kernel shouldn't be messing with the clocks. Add CLK_IGNORE_UNUSED to these clocks. Without this change, the following was observed on a Chromebook with a rk3399 (using not-yet-upstream ARM Trusted Firmware code and not-yet-upstream kernel code based on kernel-4.4): 1. We init the clock framework. 2. We start up "DDRFreq", which causes ATF to occasionally fire up the M0 for transitions. Each time ATF fires up the M0 it will turn on these clocks and each time it is done it will turn them off. 3. We finally get to the the part of the kernel that calls clk_disable_unused() and we disables the clocks. You can see the race above. Basically everything is fine as long as ARM Trusted Firmware isn't starting up the M0 at exactly the same time that the kernel is disabling unused clocks. ...but if the race happens then we go boom. Signed-off-by: Douglas Anderson <dianders@chromium.org> --- drivers/clk/rockchip/clk-rk3399.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)