On Mon, 09 Jan 2017 19:14:43 -0800 Stefan Agner <ste...@agner.ch> wrote:
> >> > >> > > >> > But, while reviewing your patch I realized this was actually unneeded > >> > (see the explanation in my previous review). > >> > > >> > > > >> > > Now it depends on cstate.enabled flag. > >> > > > >> > > So we end up with > >> > > > >> > > if (state.enabled && !cstate.enabled) > >> > > clk_preapre_enable(); > >> > > >> > Yep, and that's correct. > >> > >> And following patch: > >> http://patchwork.ozlabs.org/patch/709510/ > >> > >> address this issue. > > > > Yes, that was needed because the enable/disable path were not > > separated, and we were unconditionally writing to the IP registers > > even when the PWM was already disabled (which is probably the case > > generating the fault reported by Stefan). This is not the case anymore, > > but let's wait for Stefan to confirm this. > > With v4 as is, the kernel crashes/hangs on i.MX 7. > > The function imx_pwm_apply_v2 gets first called with state->enabled 0, > cstate->enabled 0. This branches to else and leads to a register access > with clocks disabled (and if that would succeed, also an unbalanced > disable?...) > > With the proposed change plus the additional change in the else branch > it works for me: > > @@ -192,19 +193,20 @@ static int imx_pwm_apply_v2(struct pwm_chip *chip, > struct pwm_device *pwm, > else > period_cycles = 0; > > - 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) > + if (cstate.enabled) { > imx_pwm_wait_fifo_slot(chip, pwm); > - else if (state->enabled) > + } else if (state->enabled) { > + ret = clk_prepare_enable(imx->clk_per); > + if (ret) > + return ret; > + > imx_pwm_sw_reset(chip); > + } > > writel(duty_cycles, imx->mmio_base + MX3_PWMSAR); > writel(period_cycles, imx->mmio_base + MX3_PWMPR); > @@ -218,7 +220,7 @@ static int imx_pwm_apply_v2(struct pwm_chip *chip, > struct pwm_device *pwm, > cr |= MX3_PWMCR_POUTC; > > writel(cr, imx->mmio_base + MX3_PWMCR); > - } else { > + } else if (cstate.enabled) { > writel(0, imx->mmio_base + MX3_PWMCR); > > clk_disable_unprepare(imx->clk_per); > > > This would not disable a disabled PWM anymore, I guess at normal use not > a problem. Only at bootup it could end up left on, but I guess if we > care about boot time transition we should implement get_state, but > something which we can do in a follow up patch. Yep, that's a different problem which could be addressed by implementing ->get_state(). Note that you don't necessary want to disable the PWM at boot time, in some situation, when the PWM is driving a critical device (like the VDDIODDR regulator), you want the transition between the bootloader/firmware and Linux to be as smooth as possible. Actually, 'initial state retrieval' and 'atomic changes' were added to handle this case. Stefan, one last thing, can you apply patch 2 alone and check if it doesn't introduce a regression? Thanks, Boris
