Re: [PATCH v2 02/10] gpio: aggregator: introduce basic configfs interface

[Bartosz Golaszewski]

On Mon, Feb 3, 2025 at 4:12 AM Koichiro Den <koichiro.den@xxxxxxxxxxxxx> wrote:
>
> The existing sysfs 'new_device' interface has several limitations:
> * No way to determine when GPIO aggregator creation is complete.
> * No way to retrieve errors when creating a GPIO aggregator.
> * No way to trace a GPIO line of an aggregator back to its
>   corresponding physical device.
> * The 'new_device' echo does not indicate which virtual gpiochip<N>
>   was created.
> * No way to assign names to GPIO lines exported through an aggregator.
>
> Introduce the new configfs interface for gpio-aggregator to address
> these limitations. It provides a more streamlined, modern, and
> extensible configuration method. For backward compatibility, the
> 'new_device' interface and its behaviour is retained for now.
>
> This commit implements minimal functionalities:
>
>   /config/gpio-aggregator/<name-of-your-choice>/
>   /config/gpio-aggregator/<name-of-your-choice>/live
>   /config/gpio-aggregator/<name-of-your-choice>/<lineY>/
>   /config/gpio-aggregator/<name-of-your-choice>/<lineY>/key
>   /config/gpio-aggregator/<name-of-your-choice>/<lineY>/offset
>
> Basic setup flow is:
> 1. Create a directory for a GPIO aggregator.
> 2. Create subdirectories for each line you want to instantiate.
> 3. In each line directory, configure the key and offset.
>    The key/offset semantics are as follows:
>    * If offset is >= 0:
>      - key specifies the name of the chip this GPIO belongs to
>      - offset specifies the line offset within that chip.
>    * If offset is <0:
>      - key needs to specify the GPIO line name.
> 4. Return to the aggregator's root directory and write '1' to the live
>    attribute.
>
> For example, the command in the existing kernel doc:
>
>   echo 'e6052000.gpio 19 e6050000.gpio 20-21' > new_device
>
> is equivalent to:
>
>   mkdir /sys/kernel/config/gpio-aggregator/<custom-name>
>   # Change <custom-name> to name of your choice (e.g. "aggr0")
>   cd /sys/kernel/config/gpio-aggregator/<custom-name>
>   mkdir line0 line1 line2  # Only "line<Y>" naming allowed.
>   echo e6052000.gpio > line0/key
>   echo 19            > line0/offset
>   echo e6050000.gpio > line1/key
>   echo 20            > line1/offset
>   echo e6050000.gpio > line2/key
>   echo 21            > line2/offset
>   echo 1             > live
>
> Signed-off-by: Koichiro Den <koichiro.den@xxxxxxxxxxxxx>
> ---
>  drivers/gpio/gpio-aggregator.c | 549 ++++++++++++++++++++++++++++++++-
>  1 file changed, 548 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpio-aggregator.c b/drivers/gpio/gpio-aggregator.c
> index 570cd1ff8cc2..c63cf3067ce7 100644
> --- a/drivers/gpio/gpio-aggregator.c
> +++ b/drivers/gpio/gpio-aggregator.c
> @@ -9,10 +9,14 @@
>
>  #include <linux/bitmap.h>
>  #include <linux/bitops.h>
> +#include <linux/completion.h>
> +#include <linux/configfs.h>
>  #include <linux/ctype.h>
>  #include <linux/delay.h>
>  #include <linux/idr.h>
>  #include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/lockdep.h>
>  #include <linux/mod_devicetable.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
> @@ -34,11 +38,39 @@
>   */
>
>  struct gpio_aggregator {
> +       struct config_group group;
>         struct gpiod_lookup_table *lookups;
>         struct platform_device *pdev;
> +       struct mutex lock;
> +       int id;
> +
> +       /* Synchronize with probe */
> +       struct notifier_block bus_notifier;
> +       struct completion probe_completion;
> +       bool driver_bound;
> +
> +       /* List of gpio_aggregator_line. Always added in order */
> +       struct list_head list_head;
> +
>         char args[];
>  };
>
> +struct gpio_aggregator_line {
> +       struct config_group group;
> +       struct gpio_aggregator *parent;
> +       struct list_head entry;
> +
> +       /* Line index within the aggregator device */
> +       int idx;
> +
> +       /* GPIO chip label or line name */
> +       char *key;
> +       /* Can be negative to indicate lookup by line name */
> +       int offset;
> +
> +       enum gpio_lookup_flags flags;
> +};
> +
>  static DEFINE_MUTEX(gpio_aggregator_lock);     /* protects idr */
>  static DEFINE_IDR(gpio_aggregator_idr);
>
> @@ -61,6 +93,97 @@ static int aggr_add_gpio(struct gpio_aggregator *aggr, const char *key,
>         return 0;
>  }
>
> +static int aggr_notifier_call(struct notifier_block *nb, unsigned long action,
> +                             void *data)
> +{
> +       struct gpio_aggregator *aggr;
> +       struct device *dev = data;
> +
> +       aggr = container_of(nb, struct gpio_aggregator, bus_notifier);
> +       if (!device_match_name(dev, aggr->lookups->dev_id))
> +               return NOTIFY_DONE;
> +
> +       switch (action) {
> +       case BUS_NOTIFY_BOUND_DRIVER:
> +               aggr->driver_bound = true;
> +               break;
> +       case BUS_NOTIFY_DRIVER_NOT_BOUND:
> +               aggr->driver_bound = false;
> +               break;
> +       default:
> +               return NOTIFY_DONE;
> +       }
> +
> +       complete(&aggr->probe_completion);
> +       return NOTIFY_OK;
> +}

Suggestion: this is the third time we're seeing this mechanism being
used (after gpio-sim and gpio-virtuser). Maybe it's time to try and
abstract it as much of the code is shared?

The rest looks good to me.

Bart