Re: [PATCH v2] platform/chrome: cros_ec_chardev: Add a poll handler to receive MKBP events

[Gwendal Grignou]

On Mon, Sep 2, 2019 at 9:24 AM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Mon, Sep 02, 2019 at 06:08:48PM +0200, Enric Balletbo i Serra wrote:
> > Allow to poll on the cros_ec device to receive the MKBP events.
> >
> > The /dev/cros_[ec|fp|..] file operations now implements the poll
> > operation. The userspace can now receive specific MKBP events by doing
> > the
> > following:
> > - Open the /dev/cros_XX file.
> > - Call the CROS_EC_DEV_IOCEVENTMASK ioctl with the bitmap of the MKBP
> >   events it wishes to receive as argument.
> > - Poll on the file descriptor.
> > - When it gets POLLIN, do a read on the file descriptor, the first
> >   queued event will be returned (using the struct
> >   ec_response_get_next_event format: one byte of event type, then
> >   the payload).
> >
> > The read() operation returns at most one event even if there are several
> > queued, and it might be truncated if the buffer is smaller than the
> > event (but the caller should know the maximum size of the events it is
> > reading).
> >
> > read() used to return the EC version string, it still does it when no
> > event mask or an empty event is set for backward compatibility (despite
> > nobody really using this feature).
> >
> > This will be used, for example, by the userspace daemon to receive and
> > treat the EC_MKBP_EVENT_FINGERPRINT sent by the FP MCU.
> >
>
> Acked-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Reviewed-by: Gwendal Grignou <gwendal@xxxxxxxxxxxx>
>
> > Signed-off-by: Vincent Palatin <vpalatin@xxxxxxxxxxxx>
> > Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
> > ---
> > Note that this patch depends on the immutable branch [1] to apply
> > cleanly.
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git/log/?h=ib-mfd-extcon-hid-i2c-iio-input-media-chrome-power-pwm-rtc-sound-5.4
> >
> >
> > Changes in v2:
> > - Moved the code to the cros_ec_chardev driver.
> >
> >  drivers/platform/chrome/cros_ec_chardev.c     | 177 +++++++++++++++++-
> >  include/linux/platform_data/cros_ec_chardev.h |   1 +
> >  2 files changed, 173 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/platform/chrome/cros_ec_chardev.c b/drivers/platform/chrome/cros_ec_chardev.c
> > index 08abd7e5c7bf..eabb1fe85688 100644
> > --- a/drivers/platform/chrome/cros_ec_chardev.c
> > +++ b/drivers/platform/chrome/cros_ec_chardev.c
> > @@ -16,21 +16,42 @@
> >  #include <linux/mfd/cros_ec.h>
> >  #include <linux/miscdevice.h>
> >  #include <linux/module.h>
> > +#include <linux/notifier.h>
> >  #include <linux/platform_data/cros_ec_chardev.h>
> >  #include <linux/platform_data/cros_ec_commands.h>
> >  #include <linux/platform_data/cros_ec_proto.h>
> >  #include <linux/platform_device.h>
> > +#include <linux/poll.h>
> >  #include <linux/slab.h>
> >  #include <linux/types.h>
> >  #include <linux/uaccess.h>
> >
> >  #define DRV_NAME             "cros-ec-chardev"
> >
> > +/* Arbitrary bounded size for the event queue */
> > +#define CROS_MAX_EVENT_LEN   PAGE_SIZE
> > +
> >  struct chardev_data {
> >       struct cros_ec_dev *ec_dev;
> >       struct miscdevice misc;
> >  };
> >
> > +struct chardev_priv {
> > +     struct cros_ec_dev *ec_dev;
> > +     struct notifier_block notifier;
> > +     wait_queue_head_t wait_event;
> > +     unsigned long event_mask;
> > +     struct list_head events;
> > +     size_t event_len;
> > +};
> > +
> > +struct ec_event {
> > +     struct list_head node;
> > +     size_t size;
> > +     u8 event_type;
> > +     u8 data[0];
> > +};
> > +
> >  static int ec_get_version(struct cros_ec_dev *ec, char *str, int maxlen)
> >  {
> >       static const char * const current_image_name[] = {
> > @@ -69,6 +90,71 @@ static int ec_get_version(struct cros_ec_dev *ec, char *str, int maxlen)
> >       return ret;
> >  }
> >
> > +static int ec_mkbp_event(struct notifier_block *nb,
> > +                      unsigned long queued_during_suspend,
> > +                      void *_notify)
nit: call it cros_ec_chardev_mkbp_event()  to fit other functions
naming convention. Change only if a v3 is needed.
> > +{
> > +     struct chardev_priv *priv = container_of(nb, struct chardev_priv,
> > +                                              notifier);
> > +     struct cros_ec_device *ec_dev = priv->ec_dev->ec_dev;
> > +     struct ec_event *event;
> > +     unsigned long event_bit = 1 << ec_dev->event_data.event_type;
> > +     int total_size = sizeof(*event) + ec_dev->event_size;
> > +
> > +     if (!(event_bit & priv->event_mask) ||
> > +         (priv->event_len + total_size) > CROS_MAX_EVENT_LEN)
> > +             return NOTIFY_DONE;
> > +
> > +     event = kzalloc(total_size, GFP_KERNEL);
> > +     if (!event)
> > +             return NOTIFY_DONE;
> > +
> > +     event->size = ec_dev->event_size;
> > +     event->event_type = ec_dev->event_data.event_type;
> > +     memcpy(event->data, &ec_dev->event_data.data, ec_dev->event_size);
> > +
> > +     spin_lock(&priv->wait_event.lock);
> > +     list_add_tail(&event->node, &priv->events);
> > +     priv->event_len += total_size;
> > +     wake_up_locked(&priv->wait_event);
> > +     spin_unlock(&priv->wait_event.lock);
> > +
> > +     return NOTIFY_OK;
> > +}
> > +
> > +static struct ec_event *ec_fetch_event(struct chardev_priv *priv, bool fetch,
> > +                                    bool block)
nit: cros_ec_chardev_fetch_event()
> > +{
> > +     struct ec_event *event;
> > +     int err;
> > +
> > +     spin_lock(&priv->wait_event.lock);
> > +     if (!block && list_empty(&priv->events)) {
> > +             event = ERR_PTR(-EWOULDBLOCK);
> > +             goto out;
> > +     }
> > +
> > +     if (!fetch) {
> > +             event = NULL;
> > +             goto out;
> > +     }
> > +
> > +     err = wait_event_interruptible_locked(priv->wait_event,
> > +                                           !list_empty(&priv->events));
> > +     if (err) {
> > +             event = ERR_PTR(err);
> > +             goto out;
> > +     }
> > +
> > +     event = list_first_entry(&priv->events, struct ec_event, node);
> > +     list_del(&event->node);
> > +     priv->event_len -= sizeof(*event) + event->size;
> > +
> > +out:
> > +     spin_unlock(&priv->wait_event.lock);
> > +     return event;
> > +}
> > +
> >  /*
> >   * Device file ops
> >   */
> > @@ -76,11 +162,40 @@ static int cros_ec_chardev_open(struct inode *inode, struct file *filp)
> >  {
> >       struct miscdevice *mdev = filp->private_data;
> >       struct cros_ec_dev *ec_dev = dev_get_drvdata(mdev->parent);
> > +     struct chardev_priv *priv;
> > +     int ret;
> > +
> > +     priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> > +     if (!priv)
> > +             return -ENOMEM;
> >
> > -     filp->private_data = ec_dev;
> > +     priv->ec_dev = ec_dev;
> > +     filp->private_data = priv;
> > +     INIT_LIST_HEAD(&priv->events);
> > +     init_waitqueue_head(&priv->wait_event);
> >       nonseekable_open(inode, filp);
> >
> > -     return 0;
> > +     priv->notifier.notifier_call = ec_mkbp_event;
> > +     ret = blocking_notifier_chain_register(&ec_dev->ec_dev->event_notifier,
> > +                                            &priv->notifier);
> > +     if (ret) {
> > +             dev_err(ec_dev->dev, "failed to register event notifier\n");
> > +             kfree(priv);
> > +     }
> > +
> > +     return ret;
> > +}
> > +
> > +static __poll_t cros_ec_chardev_poll(struct file *filp, poll_table *wait)
> > +{
> > +     struct chardev_priv *priv = filp->private_data;
> > +
> > +     poll_wait(filp, &priv->wait_event, wait);
> > +
> > +     if (list_empty(&priv->events))
> > +             return 0;
> > +
> > +     return EPOLLIN | EPOLLRDNORM;
> >  }
> >
> >  static ssize_t cros_ec_chardev_read(struct file *filp, char __user *buffer,
> > @@ -88,14 +203,42 @@ static ssize_t cros_ec_chardev_read(struct file *filp, char __user *buffer,
> >  {
> >       char msg[sizeof(struct ec_response_get_version) +
> >                sizeof(CROS_EC_DEV_VERSION)];
> > -     struct cros_ec_dev *ec = filp->private_data;
> > +     struct chardev_priv *priv = filp->private_data;
> > +     struct cros_ec_dev *ec_dev = priv->ec_dev;
> >       size_t count;
> >       int ret;
> >
> > +     if (priv->event_mask) { /* queued MKBP event */
> > +             struct ec_event *event;
> > +
> > +             event = ec_fetch_event(priv, length != 0,
> > +                                    !(filp->f_flags & O_NONBLOCK));
> > +             if (IS_ERR(event))
> > +                     return PTR_ERR(event);
> > +             /*
> > +              * length == 0 is special - no IO is done but we check
> > +              * for error conditions.
> > +              */
> > +             if (length == 0)
> > +                     return 0;
> > +
> > +             /* The event is 1 byte of type plus the payload */
> > +             count = min(length, event->size + 1);
> > +             ret = copy_to_user(buffer, &event->event_type, count);
> > +             kfree(event);
> > +             if (ret) /* the copy failed */
> > +                     return -EFAULT;
> > +             *offset = count;
> > +             return count;
> > +     }
> > +
> > +     /*
> > +      * Legacy behavior if no event mask is defined
> > +      */
> >       if (*offset != 0)
> >               return 0;
> >
> > -     ret = ec_get_version(ec, msg, sizeof(msg));
> > +     ret = ec_get_version(ec_dev, msg, sizeof(msg));
> >       if (ret)
> >               return ret;
> >
> > @@ -108,6 +251,24 @@ static ssize_t cros_ec_chardev_read(struct file *filp, char __user *buffer,
> >       return count;
> >  }
> >
> > +static int cros_ec_chardev_release(struct inode *inode, struct file *filp)
> > +{
> > +     struct chardev_priv *priv = filp->private_data;
> > +     struct cros_ec_dev *ec_dev = priv->ec_dev;
> > +     struct ec_event *event, *e;
> > +
> > +     blocking_notifier_chain_unregister(&ec_dev->ec_dev->event_notifier,
> > +                                        &priv->notifier);
> > +
> > +     list_for_each_entry_safe(event, e, &priv->events, node) {
> > +             list_del(&event->node);
> > +             kfree(event);
> > +     }
> > +     kfree(priv);
> > +
> > +     return 0;
> > +}
> > +
> >  /*
> >   * Ioctls
> >   */
> > @@ -181,7 +342,8 @@ static long cros_ec_chardev_ioctl_readmem(struct cros_ec_dev *ec,
> >  static long cros_ec_chardev_ioctl(struct file *filp, unsigned int cmd,
> >                                  unsigned long arg)
> >  {
> > -     struct cros_ec_dev *ec = filp->private_data;
> > +     struct chardev_priv *priv = filp->private_data;
> > +     struct cros_ec_dev *ec = priv->ec_dev;
> >
> >       if (_IOC_TYPE(cmd) != CROS_EC_DEV_IOC)
> >               return -ENOTTY;
> > @@ -191,6 +353,9 @@ static long cros_ec_chardev_ioctl(struct file *filp, unsigned int cmd,
> >               return cros_ec_chardev_ioctl_xcmd(ec, (void __user *)arg);
> >       case CROS_EC_DEV_IOCRDMEM:
> >               return cros_ec_chardev_ioctl_readmem(ec, (void __user *)arg);
> > +     case CROS_EC_DEV_IOCEVENTMASK:
> > +             priv->event_mask = arg;
> > +             return 0;
> >       }
> >
> >       return -ENOTTY;
> > @@ -198,7 +363,9 @@ static long cros_ec_chardev_ioctl(struct file *filp, unsigned int cmd,
> >
> >  static const struct file_operations chardev_fops = {
> >       .open           = cros_ec_chardev_open,
> > +     .poll           = cros_ec_chardev_poll,
> >       .read           = cros_ec_chardev_read,
> > +     .release        = cros_ec_chardev_release,
> >       .unlocked_ioctl = cros_ec_chardev_ioctl,
> >  #ifdef CONFIG_COMPAT
> >       .compat_ioctl   = cros_ec_chardev_ioctl,
> > diff --git a/include/linux/platform_data/cros_ec_chardev.h b/include/linux/platform_data/cros_ec_chardev.h
> > index 973b2615aa02..7de8faaf77df 100644
> > --- a/include/linux/platform_data/cros_ec_chardev.h
> > +++ b/include/linux/platform_data/cros_ec_chardev.h
> > @@ -33,5 +33,6 @@ struct cros_ec_readmem {
> >  #define CROS_EC_DEV_IOC       0xEC
> >  #define CROS_EC_DEV_IOCXCMD   _IOWR(CROS_EC_DEV_IOC, 0, struct cros_ec_command)
> >  #define CROS_EC_DEV_IOCRDMEM  _IOWR(CROS_EC_DEV_IOC, 1, struct cros_ec_readmem)
> > +#define CROS_EC_DEV_IOCEVENTMASK _IO(CROS_EC_DEV_IOC, 2)
> >
> >  #endif /* _CROS_EC_DEV_H_ */
> > --
> > 2.20.1
> >
>
> --
> With Best Regards,
> Andy Shevchenko
>
>