Messages in this thread | | | Subject | Re: [v13 2/2] pwm: Add Aspeed ast2600 PWM support | From | Philipp Zabel <> | Date | Wed, 01 Dec 2021 10:11:42 +0100 |
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Hi Billy,
On Wed, 2021-12-01 at 03:30 +0000, Billy Tsai wrote: > Hi Philipp, > > On 2021/11/30, 5:52 PM, "Philipp Zabel" <p.zabel@pengutronix.de> wrote: > > On Mon, 2021-11-29 at 14:43 +0800, Billy Tsai wrote: > [...] > > > + ret = clk_prepare_enable(priv->clk); > > > + if (ret) > > > + return dev_err_probe(dev, ret, "Couldn't enable clock\n"); > > > + > > > + ret = reset_control_deassert(priv->reset); > > > + if (ret) { > > > + dev_err_probe(dev, ret, "Couldn't deassert reset control\n"); > > > + goto err_disable_clk; > > > + } > > > Is there any reason to keep the clocks running and the controller out of > > reset while the PWM outputs are disabled? > > Can you tell me about your concerns with this process?
No particular concerns, just curiosity.
> In my opinion, they are used to provide the clock and de-assert the reset of the PWM engine. If we didn't release > them in probe stage the CPU can't and shouldn't read the register of the PWM engine when call the get_state. > Assume that we want to adjust them dynamically, the driver needs to add more conditions to check and keep the status > of each PWM channel, which is not a good deal for the server platform.
Thanks. I don't know the hardware, so I have no idea whether disabling the clocks would even save a measurable (let alone appreciable) amount of power.
I've just seen other PWM drivers use runtime PM or enable/disable clocks dynamically, and wondered why this one doesn't.
regards Philipp
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