Messages in this thread | | | Date | Tue, 3 Jan 2017 23:46:58 +0100 | From | Lukasz Majewski <> | Subject | Re: [PATCH v3 RESEND 07/11] pwm: imx: Provide atomic PWM support for i.MX PWMv2 |
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Hi Boris,
> On Tue, 3 Jan 2017 23:01:11 +0100 > Lukasz Majewski <lukma@denx.de> wrote: > > > Hi Boris, Stefan, > > > > > On Tue, 03 Jan 2017 09:29:40 -0800 > > > Stefan Agner <stefan@agner.ch> wrote: > > > > > > > On 2017-01-03 04:46, Boris Brezillon wrote: > > > > <snip> > > > > >> > Well, regarding the imx_pwm_apply_v2() suggested by > > > > >> > Stefan, I think we both agreed that most of the code was > > > > >> > unneeded when all we want to do is disable the PWM. > > > > >> > > > > >> So for the PATCH 7/11 we fix the issue with recalculating > > > > >> clocks when we want to disable PWM. > > > > >> > > > > >> if (state->enabled) { > > > > >> c = clk_get_rate(imx->clk_per); > > > > >> c *= state->period; > > > > >> > > > > >> do_div(c, 1000000000); > > > > >> period_cycles = c; > > > > >> > > > > >> prescale = period_cycles / 0x10000 + 1; > > > > >> > > > > >> period_cycles /= prescale; > > > > >> c = (unsigned long long)period_cycles * > > > > >> state->duty_cycle; > > > > >> do_div(c, state->period); > > > > >> duty_cycles = c; > > > > >> > > > > >> /* > > > > >> * According to imx pwm RM, the real period > > > > >> value > > > > >> * should be PERIOD value in PWMPR plus 2. > > > > >> */ > > > > >> if (period_cycles > 2) > > > > >> period_cycles -= 2; > > > > >> else > > > > >> period_cycles = 0; > > > > >> > > > > >> /* > > > > >> * Enable the clock if the PWM is not already > > > > >> * enabled. > > > > >> */ > > > > >> if (!cstate.enabled) { > > > > >> ret = > > > > >> clk_prepare_enable(imx->clk_per); if (ret) > > > > >> return ret; > > > > >> } > > > > >> > > > > >> /* > > > > >> * Wait for a free FIFO slot if the PWM is > > > > >> already > > > > >> * enabled, and flush the FIFO if the PWM was > > > > >> disabled > > > > >> * and is about to be enabled. > > > > >> */ > > > > >> if (cstate.enabled) > > > > >> imx_pwm_wait_fifo_slot(chip, pwm); > > > > >> else > > > > >> imx_pwm_sw_reset(chip); > > > > >> > > > > >> writel(duty_cycles, imx->mmio_base + > > > > >> MX3_PWMSAR); writel(period_cycles, imx->mmio_base + > > > > >> MX3_PWMPR); > > > > >> > > > > >> writel(MX3_PWMCR_PRESCALER(prescale) | > > > > >> MX3_PWMCR_DOZEEN | MX3_PWMCR_WAITEN | > > > > >> MX3_PWMCR_DBGEN | > > > > >> MX3_PWMCR_CLKSRC_IPG_HIGH | MX3_PWMCR_EN, > > > > >> imx->mmio_base + MX3_PWMCR); > > > > >> } else { > > > > >> > > > > >> writel(0, imx->mmio_base + MX3_PWMCR); > > > > >> > > > > >> /* Disable the clock if the PWM is currently > > > > >> enabled. */ if (cstate.enabled) > > > > >> clk_disable_unprepare(imx->clk_per); > > > > >> } > > > > >> > > > > >> > > > > > > > > > > Yep. > > > > > > > > > > > > > This looks like a good transformation of the current Patch 7, > > > > but once you merge my patch, it will look slightly > > > > different... > > > > > > Yes. I think we should just unconditionally enable/disable the > > > per_clk at function entry/exit. The prepare_enable() call is > > > almost free when the clk is already enabled, so it's not like > > > we're adding a huge overhead by doing that. > > > > So in the above snippet we should replace: > > > > if (!cstate.enabled) { > > ret = clk_prepare_enable(imx->clk_per); > > if (ret) > > return ret; > > } > > > > with > > ret = clk_prepare_enable(imx->clk_per); > > if (ret) > > return ret; > > > > And > > > > if (cstate.enabled) > > clk_disable_unprepare(imx->clk_per); > > > > with > > clk_disable_unprepare(imx->clk_per); > > That's what I had in mind.
OK.
> > > > > > > > > > > > > > >> > > > > >> > > > > > >> > My concern was more about the way PWM changes are applied > > > > >> > (->apply() returns before the change is actually applied), > > > > >> > but I agreed that it could be fixed later on (if other > > > > >> > people think it's really needed), since the existing code > > > > >> > already handles it this way. > > > > >> > > > > >> This is the issue with FIFO setting - but for now we do not > > > > >> deal with it. > > > > > > > > > > Exactly. > > > > > > > > > >> > > > > >> > > > > > >> > > No clear decision what to change until today when Stefan > > > > >> > > prepared separate (concise) patch (now I see what is the > > > > >> > > problem). > > > > >> > > > > > >> > The patch proposed by Stefan is addressing a different > > > > >> > problem: the periph clock has to be enabled before > > > > >> > accessing registers. > > > > >> > > > > >> So for this reason Stefan's patch [1] always enable the > > > > >> clock no matter if PWM clock is generated or not. > > > > > > > > > > Yes. > > > > > > > > > >> > > > > >> > > > > > >> > > > > > > >> > > > > > > > >> > > > Same goes for the regression introduced in patch 2: I > > > > >> > > > think it's better to keep things bisectable on all > > > > >> > > > platforms (even if it appeared to work by chance on > > > > >> > > > imx7, it did work before this change). > > > > >> > > > > > > >> > > Could you be more specific about your idea to solve this > > > > >> > > problem? > > > > >> > > > > > >> > Stefan already provided a patch, I just think it should be > > > > >> > fixed before patch 2 to avoid breaking bisectibility. > > > > >> > > > > >> My idea is as follows: > > > > >> > > > > >> I will drop patch v2 (prepared by Sasha) and then squash > > > > >> Stefan's patch [1] to patch 7/11. The "old" ipg enable code > > > > >> will be removed with other not needed code during > > > > >> conversion. > > > > > > > > > > How about keeping patch 2 but enabling/disabling the periph > > > > > clk in imx_pwm_config() instead of completely dropping the > > > > > enable/disable clk sequence. > > > > > > > > > > In patch 7 you just add the logic we talked about earlier: > > > > > unconditionally enable the periph clk when entering the > > > > > imx_pwm_apply_v2() function and disable it before leaving the > > > > > function. > > > > > > > > > > This way you can preserve bisectibility and still get rid of > > > > > the ipg clk. > > > > > > > > > > Stefan, what's your opinion? > > > > > > > > We will get rid of the ipg clocks anyway in patch 8 (which > > > > removes those functions completely). > > > > > > > > So I think Lukasz approach should be fine, just drop patch 2 and > > > > squash my patch into patch 7. > > > > > > Well, the end result will be same (ipg_clk will be gone after > > > patch 8), but then it's hard to track why this clock suddenly > > > disappeared. I still think it's worth adding an extra commit > > > explaining that enabling the per_clk before accessing IP > > > registers is needed on some platforms (imx7), and that IPG clk is > > > actually not required until we start using it as a source for the > > > PWM signal generation. > > > > > > Maybe I'm the only one to think so. In this case, feel free to > > > drop patch 2. > > > > If you feel really bad about this issue, then we can drop patch 2 > > and: > > > > reorganize patch 7/11 to > > - keep code, which adds imx_pwm_apply_v2() function code (just > > moves it as is) > > - remove .apply = imx_pwm_apply_v2 entry from pwm_ops structure. > > > > > > On top of it add patch to enable/disable unconditionally the > > imx->clk_per clock to avoid problems on imx7 (and state them in > > commit message). > > > > Then we add separate patch with > > .apply = imx_pwm_apply_v2 to pwm_ops structure to enable "new" > > atomic approach. > > > > And at last we apply patch 8/11, which removes the code for old (non > > atomic) behaviour. > > > > All the issues are documented in this way on the cost of having > > "dead" (I mean not used) imx_pwm_apply_v2() for two commits. > > > > This looks even more complicated. > Sorry, but I don't see the problem with modifying patch 2 to enable > per_clk instead of ipg_clk. Can you explain what's bothering you?
But in patch 2: "pwm: imx: remove ipg clock"
we _remove_ the clk_ipg from imx_pwm_config() and imx_pwm_probe(), so I'm quite puzzled with your above statement.
> > If you really want to do the change after patch 7, fine, but in this > case, keep the existing logic: enable/disable ipg_clk in > imx_pwm_apply_v2() until you drop the ipg_clk and replace the ipg_clk > enable/disable sequence by the equivalent enable/disable per_clk one. >
Frankly, I do agree with Stefan here - we should drop patch 2, squash all changes (including imx7 clock issues) to patch 7 (including verbose commit message) and remove the non-atomic code in patch 8.
Best regards,
Lukasz Majewski
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