Messages in this thread | | | Date | Thu, 13 Oct 2022 13:49:49 +0800 | From | Tzung-Bi Shih <> | Subject | Re: [PATCH v5 1/1] platform/chrome: add a driver for HPS |
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On Wed, Oct 12, 2022 at 09:29:03PM -0700, Dan Callaghan wrote: > Excerpts from Tzung-Bi Shih’s message of 2022-10-12 19:46:51 +1100: > > On Wed, Oct 12, 2022 at 03:09:18PM +1100, Dan Callaghan wrote: > > > + hps->enable_gpio = devm_gpiod_get(&client->dev, "enable", GPIOD_OUT_HIGH); > > > + if (IS_ERR(hps->enable_gpio)) { > > > + ret = PTR_ERR(hps->enable_gpio); > > > + dev_err(&client->dev, "failed to get enable gpio: %d\n", ret); > > > + return ret; > > > + } > > > + > > > + ret = misc_register(&hps->misc_device); > > > + if (ret) { > > > + dev_err(&client->dev, "failed to initialize misc device: %d\n", ret); > > > + return ret; > > > + } > > > + > > > + hps_set_power(hps, false); > > > > IIUC, the GPIO will raise to HIGH in the first place, and then fall > > to LOW until here. Is it an expected behavior? How about gpiod_get() > > with GPIOD_OUT_LOW? > > It might seem a little unusual, but it is intentional. The enable line is > already high when we enter the kernel from firmware. Acquiring the GPIO > line with GPIOD_OUT_HIGH preserves its existing state (high) in case later > steps fail. > > We power off the periphal only once the driver is successfully bound and has > taken control of its power state.
I see. Please put some context comments before calling devm_gpiod_get().
> > > +static int hps_i2c_remove(struct i2c_client *client) > > > +{ > > > + struct hps_drvdata *hps = i2c_get_clientdata(client); > > > + > > > + pm_runtime_disable(&client->dev); > > > + misc_deregister(&hps->misc_device); > > > + hps_set_power(hps, true); > > > > Why does it need to raise the GPIO again when removing the device? > > Similar to the above, we want to preserve the default power state > (i.e. powered on) whenever the driver is not bound to the device. > > This behaviour made sense to us mainly because we were originally controlling > the peripheral entirely from userspace, so it was always powered on by default. > > Do you think this behaviour is acceptable, or do we need to change it?
I think it's fine. Please put some context comments before calling hps_set_power().
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