On Mon, Jun 21, 2021 at 8:25 PM Mauri Sandberg <maukka@xxxxxxxxxxxx> wrote:
>
> Adds support for a building cascades of GPIO lines. That is, it allows
for building
> setups when there is one upstream line and multiple cascaded lines, out
> of which one can be chosen at a time. The status of the upstream line
> can be conveyd to the selected cascaded line or, vice versa, the status
conveyed
> of the cascaded line can be conveyed to the upstream line.
>
> A gpio-mux is being used to select, which cascaded GPIO line is being
> used at any given time.
>
> At the moment only input direction is supported. In future it should be
> possible to add support for output direction, too.
Since in parallel there is a discussion about the virtio-gpio
interface, how will this work with it?
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * A generic GPIO cascade driver
> + *
> + * Copyright (C) 2021 Mauri Sandberg <maukka@xxxxxxxxxxxx>
> + *
> + * This allows building cascades of GPIO lines in a manner illustrated
> + * below:
> + *
> + * /|---- Cascaded GPIO line 0
> + * Upstream | |---- Cascaded GPIO line 1
> + * GPIO line ----+ | .
> + * | | .
> + * \|---- Cascaded GPIO line n
> + *
> + * A gpio-mux is being used to select, which cascaded line is being
> + * addressed at any given time.
> + *
> + * At the moment only input mode is supported due to lack of means for
> + * testing output functionality. At least theoretically output should be
> + * possible with an open drain constructions.
> + */
...
> +static int gpio_cascade_get_value(struct gpio_chip *gc, unsigned int offset)
> +{
> + struct gpio_cascade *cas;
> + int ret;
> + cas = chip_to_cascade(gc);
Doing this in the definition block above will save a LOC.
> + ret = mux_control_select(cas->mux_control, offset);
> + if (ret)
> + return ret;
> +
> + ret = gpiod_get_value(cas->upstream_line);
> + mux_control_deselect(cas->mux_control);
> + return ret;
> +}
...
> + struct device_node *np = pdev->dev.of_node;
Nope, see below.
...
> + cas = devm_kzalloc(dev, sizeof(struct gpio_cascade), GFP_KERNEL);
sizeof(*cas)
> + if (cas == NULL)
if (!cas)
> + return -ENOMEM;
...
> + mc = devm_mux_control_get(dev, NULL);
> + if (IS_ERR(mc)) {
> + err = (int) PTR_ERR(mc);
> + if (err != -EPROBE_DEFER)
> + dev_err(dev, "unable to get mux-control: %d\n", err);
> + return err;
Oh là là! No, the explicit castings are bad. besides the fact that all
above can be replaced by
return dev_err_probe(...);
> + }
> +
> + cas->mux_control = mc;
> + upstream = devm_gpiod_get(dev, "upstream", GPIOD_IN);
> + if (IS_ERR(upstream)) {
> + err = (int) PTR_ERR(upstream);
> + dev_err(dev, "unable to claim upstream GPIO line: %d\n", err);
No castings. Use proper printf() specifiers.
> + return err;
> + }
...
> + gc->of_node = np;
This should be guarded by CONFIG_OF_GPIO.
And no need to use the np temporary variable for one use like this.
...
> + err = gpiochip_add(&cas->gpio_chip);
Why not the devm variant?
> + if (err) {
> + dev_err(dev, "unable to add gpio chip, err=%d\n", err);
> + return err;
> + }
...
> + dev_info(dev, "registered %u cascaded GPIO lines\n", gc->ngpio);
No, we don't pollute logs when everything is fine.
...
> +static const struct of_device_id gpio_cascade_id[] = {
> + {
> + .compatible = "gpio-cascade",
> + .data = NULL,
Redundant.
> + },
All above may consume only a single LOC.
> + { /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, gpio_cascade_id);
--
With Best Regards,
Andy Shevchenko
