usb: gadget: hid: allow dynamic interval configuration via configfs

This patch enhances the HID gadget driver to support dynamic configuration
of the interrupt polling interval (bInterval) via configfs.  A new
‘interval’ attribute is exposed under each HID function’s configfs
directory, and any write to it will adjust the poll rate for all endpoints
without requiring a rebuild.

When the attribute has never been written, legacy defaults are preserved:
  • Full-Speed (FS) endpoints (IN & OUT) poll every 10 ms
  • High-Speed (HS) endpoints (IN & OUT) poll every 4 micro-frames
    (~1 ms)

To implement this cleanly:
  • Add two new fields to f_hid_opts and f_hidg:
      – unsigned char interval
      – bool           interval_user_set
  • Introduce dedicated f_hid_opts_interval_show/store functions.
    The store routine parses into an unsigned int, bounds‐checks,
    assigns to opts->interval, and sets opts->interval_user_set = true.
  • Initialize opts->interval = 4 and opts->interval_user_set = false in
    hidg_alloc_inst(), then copy both into the live f_hidg instance in
    hidg_alloc().
  • In hidg_bind(), set each endpoint’s bInterval based on whether the
  user has written the attribute:
      – If interval_user_set == false, use FS=10 / HS=4
      – If interval_user_set == true, use the user’s value for both FS
        & HS

Signed-off-by: Ben Hoff <hoff.benjamin.k@gmail.com>
Link: https://lore.kernel.org/r/20250429182809.811786-1-hoff.benjamin.k@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
index 1bc40fc0ccf77b30129c728fd2bae3c258e21763..1b2a363f31778b5e5df61373e0a31dbf278f86b7 100644 (file)
--- a/drivers/usb/gadget/function/f_hid.c
+++ b/drivers/usb/gadget/function/f_hid.c
@@ -62,6 +62,9 @@ struct f_hidg {
        unsigned short                  report_desc_length;
        char                            *report_desc;
        unsigned short                  report_length;
+       unsigned char                   interval;
+       bool                            interval_user_set;
+
        /*
         * use_out_ep - if true, the OUT Endpoint (interrupt out method)
         *              will be used to receive reports from the host
@@ -157,10 +160,7 @@ static struct usb_endpoint_descriptor hidg_ss_in_ep_desc = {
        .bEndpointAddress       = USB_DIR_IN,
        .bmAttributes           = USB_ENDPOINT_XFER_INT,
        /*.wMaxPacketSize       = DYNAMIC */
-       .bInterval              = 4, /* FIXME: Add this field in the
-                                     * HID gadget configuration?
-                                     * (struct hidg_func_descriptor)
-                                     */
+       /*.bInterval            = DYNAMIC */
 };
 
 static struct usb_ss_ep_comp_descriptor hidg_ss_in_comp_desc = {
@@ -178,10 +178,7 @@ static struct usb_endpoint_descriptor hidg_ss_out_ep_desc = {
        .bEndpointAddress       = USB_DIR_OUT,
        .bmAttributes           = USB_ENDPOINT_XFER_INT,
        /*.wMaxPacketSize       = DYNAMIC */
-       .bInterval              = 4, /* FIXME: Add this field in the
-                                     * HID gadget configuration?
-                                     * (struct hidg_func_descriptor)
-                                     */
+       /*.bInterval            = DYNAMIC */
 };
 
 static struct usb_ss_ep_comp_descriptor hidg_ss_out_comp_desc = {
@@ -219,10 +216,7 @@ static struct usb_endpoint_descriptor hidg_hs_in_ep_desc = {
        .bEndpointAddress       = USB_DIR_IN,
        .bmAttributes           = USB_ENDPOINT_XFER_INT,
        /*.wMaxPacketSize       = DYNAMIC */
-       .bInterval              = 4, /* FIXME: Add this field in the
-                                     * HID gadget configuration?
-                                     * (struct hidg_func_descriptor)
-                                     */
+       /* .bInterval           = DYNAMIC */
 };
 
 static struct usb_endpoint_descriptor hidg_hs_out_ep_desc = {
@@ -231,10 +225,7 @@ static struct usb_endpoint_descriptor hidg_hs_out_ep_desc = {
        .bEndpointAddress       = USB_DIR_OUT,
        .bmAttributes           = USB_ENDPOINT_XFER_INT,
        /*.wMaxPacketSize       = DYNAMIC */
-       .bInterval              = 4, /* FIXME: Add this field in the
-                                     * HID gadget configuration?
-                                     * (struct hidg_func_descriptor)
-                                     */
+       /*.bInterval            = DYNAMIC */
 };
 
 static struct usb_descriptor_header *hidg_hs_descriptors_intout[] = {
@@ -260,10 +251,7 @@ static struct usb_endpoint_descriptor hidg_fs_in_ep_desc = {
        .bEndpointAddress       = USB_DIR_IN,
        .bmAttributes           = USB_ENDPOINT_XFER_INT,
        /*.wMaxPacketSize       = DYNAMIC */
-       .bInterval              = 10, /* FIXME: Add this field in the
-                                      * HID gadget configuration?
-                                      * (struct hidg_func_descriptor)
-                                      */
+       /*.bInterval            = DYNAMIC */
 };
 
 static struct usb_endpoint_descriptor hidg_fs_out_ep_desc = {
@@ -272,10 +260,7 @@ static struct usb_endpoint_descriptor hidg_fs_out_ep_desc = {
        .bEndpointAddress       = USB_DIR_OUT,
        .bmAttributes           = USB_ENDPOINT_XFER_INT,
        /*.wMaxPacketSize       = DYNAMIC */
-       .bInterval              = 10, /* FIXME: Add this field in the
-                                      * HID gadget configuration?
-                                      * (struct hidg_func_descriptor)
-                                      */
+       /*.bInterval            = DYNAMIC */
 };
 
 static struct usb_descriptor_header *hidg_fs_descriptors_intout[] = {
@@ -1217,6 +1202,16 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
        hidg_hs_in_ep_desc.wMaxPacketSize = cpu_to_le16(hidg->report_length);
        hidg_fs_in_ep_desc.wMaxPacketSize = cpu_to_le16(hidg->report_length);
        hidg_ss_out_ep_desc.wMaxPacketSize = cpu_to_le16(hidg->report_length);
+
+       /* IN endpoints: FS default=10ms, HS default=4µ-frame; user override if set */
+       if (!hidg->interval_user_set) {
+               hidg_fs_in_ep_desc.bInterval = 10;
+               hidg_hs_in_ep_desc.bInterval = 4;
+       } else {
+               hidg_fs_in_ep_desc.bInterval = hidg->interval;
+               hidg_hs_in_ep_desc.bInterval = hidg->interval;
+       }
+
        hidg_ss_out_comp_desc.wBytesPerInterval =
                                cpu_to_le16(hidg->report_length);
        hidg_hs_out_ep_desc.wMaxPacketSize = cpu_to_le16(hidg->report_length);
@@ -1239,19 +1234,27 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
        hidg_ss_out_ep_desc.bEndpointAddress =
                hidg_fs_out_ep_desc.bEndpointAddress;
 
-       if (hidg->use_out_ep)
+       if (hidg->use_out_ep) {
+               /* OUT endpoints: same defaults (FS=10, HS=4) unless user set */
+               if (!hidg->interval_user_set) {
+                       hidg_fs_out_ep_desc.bInterval = 10;
+                       hidg_hs_out_ep_desc.bInterval = 4;
+               } else {
+                       hidg_fs_out_ep_desc.bInterval = hidg->interval;
+                       hidg_hs_out_ep_desc.bInterval = hidg->interval;
+               }
                status = usb_assign_descriptors(f,
-                       hidg_fs_descriptors_intout,
-                       hidg_hs_descriptors_intout,
-                       hidg_ss_descriptors_intout,
-                       hidg_ss_descriptors_intout);
-       else
+                           hidg_fs_descriptors_intout,
+                           hidg_hs_descriptors_intout,
+                           hidg_ss_descriptors_intout,
+                           hidg_ss_descriptors_intout);
+       } else {
                status = usb_assign_descriptors(f,
                        hidg_fs_descriptors_ssreport,
                        hidg_hs_descriptors_ssreport,
                        hidg_ss_descriptors_ssreport,
                        hidg_ss_descriptors_ssreport);
-
+       }
        if (status)
                goto fail;
 
@@ -1423,6 +1426,53 @@ end:
 
 CONFIGFS_ATTR(f_hid_opts_, report_desc);
 
+static ssize_t f_hid_opts_interval_show(struct config_item *item, char *page)
+{
+       struct f_hid_opts *opts = to_f_hid_opts(item);
+       int result;
+
+       mutex_lock(&opts->lock);
+       result = sprintf(page, "%d\n", opts->interval);
+       mutex_unlock(&opts->lock);
+
+       return result;
+}
+
+static ssize_t f_hid_opts_interval_store(struct config_item *item,
+               const char *page, size_t len)
+{
+       struct f_hid_opts *opts = to_f_hid_opts(item);
+       int ret;
+       unsigned int tmp;
+
+       mutex_lock(&opts->lock);
+       if (opts->refcnt) {
+               ret = -EBUSY;
+               goto end;
+       }
+
+       /* parse into a wider type first */
+       ret = kstrtouint(page, 0, &tmp);
+       if (ret)
+               goto end;
+
+       /* range-check against unsigned char max */
+       if (tmp > 255) {
+               ret = -EINVAL;
+               goto end;
+       }
+
+       opts->interval = (unsigned char)tmp;
+       opts->interval_user_set = true;
+       ret = len;
+
+end:
+       mutex_unlock(&opts->lock);
+       return ret;
+}
+
+CONFIGFS_ATTR(f_hid_opts_, interval);
+
 static ssize_t f_hid_opts_dev_show(struct config_item *item, char *page)
 {
        struct f_hid_opts *opts = to_f_hid_opts(item);
@@ -1437,6 +1487,7 @@ static struct configfs_attribute *hid_attrs[] = {
        &f_hid_opts_attr_protocol,
        &f_hid_opts_attr_no_out_endpoint,
        &f_hid_opts_attr_report_length,
+       &f_hid_opts_attr_interval,
        &f_hid_opts_attr_report_desc,
        &f_hid_opts_attr_dev,
        NULL,
@@ -1483,6 +1534,10 @@ static struct usb_function_instance *hidg_alloc_inst(void)
        if (!opts)
                return ERR_PTR(-ENOMEM);
        mutex_init(&opts->lock);
+
+       opts->interval = 4;
+       opts->interval_user_set = false;
+
        opts->func_inst.free_func_inst = hidg_free_inst;
        ret = &opts->func_inst;
 
@@ -1561,6 +1616,8 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
        hidg->bInterfaceProtocol = opts->protocol;
        hidg->report_length = opts->report_length;
        hidg->report_desc_length = opts->report_desc_length;
+       hidg->interval = opts->interval;
+       hidg->interval_user_set = opts->interval_user_set;
        if (opts->report_desc) {
                hidg->report_desc = kmemdup(opts->report_desc,
                                            opts->report_desc_length,

diff --git a/drivers/usb/gadget/function/u_hid.h b/drivers/usb/gadget/function/u_hid.h
index 84bb702928553923668d5c649c1f2f3979a9aff8..a9ed9720caeee6a544e226cce72444d101e81047 100644 (file)
--- a/drivers/usb/gadget/function/u_hid.h
+++ b/drivers/usb/gadget/function/u_hid.h
@@ -25,6 +25,8 @@ struct f_hid_opts {
        unsigned short                  report_desc_length;
        unsigned char                   *report_desc;
        bool                            report_desc_alloc;
+       unsigned char                   interval;
+       bool                            interval_user_set;
 
        /*
         * Protect the data form concurrent access by read/write