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Message-ID: <CAMRc=MfcooZXBqVpbQ0ak+8LGsPDzwKSN3Zfb0eZDx1Bx4duzQ@mail.gmail.com>
Date: Tue, 4 Feb 2025 13:48:49 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Koichiro Den <koichiro.den@...onical.com>
Cc: linux-gpio@...r.kernel.org, geert+renesas@...der.be,
linus.walleij@...aro.org, maciej.borzecki@...onical.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/10] gpio: aggregator: introduce basic configfs interface
On Mon, Feb 3, 2025 at 4:12 AM Koichiro Den <koichiro.den@...onical.com> 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@...onical.com>
> ---
> 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
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