On 16/08/2021 06:05, bongsu.jeon2@xxxxxxxxx wrote:
> From: Bongsu Jeon <bongsu.jeon@xxxxxxxxxxx>
>
> In previous version, the user level virtual device application that used
> this driver should have the polling scheme to read a NCI frame.
> To remove this polling scheme, changed the driver code to use Wait Queue.
>
Subject - please prefix it with:
"nfc: virtual_ncidev: "
Also make it simpler (skipping unnecessary words like "change", "device
driver"), so:
"nfc: virtual_ncidev: use wait queue instead of polling"
> Signed-off-by: Bongsu Jeon <bongsu.jeon@xxxxxxxxxxx>
> ---
> drivers/nfc/virtual_ncidev.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/nfc/virtual_ncidev.c b/drivers/nfc/virtual_ncidev.c
> index 2ee0ec4bb739..1953904176a2 100644
> --- a/drivers/nfc/virtual_ncidev.c
> +++ b/drivers/nfc/virtual_ncidev.c
> @@ -10,6 +10,7 @@
> #include <linux/module.h>
> #include <linux/miscdevice.h>
> #include <linux/mutex.h>
> +#include <linux/wait.h>
> #include <net/nfc/nci_core.h>
>
> enum virtual_ncidev_mode {
> @@ -27,6 +28,7 @@ enum virtual_ncidev_mode {
> NFC_PROTO_ISO15693_MASK)
>
> static enum virtual_ncidev_mode state;
> +static DECLARE_WAIT_QUEUE_HEAD(wq);
> static struct miscdevice miscdev;
> static struct sk_buff *send_buff;
> static struct nci_dev *ndev;
> @@ -61,6 +63,7 @@ static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb)
> }
> send_buff = skb_copy(skb, GFP_KERNEL);
> mutex_unlock(&nci_mutex);
> + wake_up_interruptible(&wq);
>
> return 0;
> }
> @@ -76,12 +79,11 @@ static ssize_t virtual_ncidev_read(struct file *file, char __user *buf,
> {
> size_t actual_len;
>
> - mutex_lock(&nci_mutex);
> - if (!send_buff) {
> - mutex_unlock(&nci_mutex);
> + wait_event_interruptible(wq, send_buff);
> + if (!send_buff)
I think access to send_buff should still be protected by mutex. What
happens if you have to readers?
> return 0;
> - }
>
> + mutex_lock(&nci_mutex);
> actual_len = min_t(size_t, count, send_buff->len);
>
> if (copy_to_user(buf, send_buff->data, actual_len)) {
>
Best regards,
Krzysztof
