Re: [PATCH v3] usb: gadget: f_hid: optional SETUP/SET_REPORT mode

[Maciej Żenczykowski]

On Sat, Aug 21, 2021 at 3:40 PM Maxim Devaev <mdevaev@xxxxxxxxx> wrote:
>
> f_hid provides the OUT Endpoint as only way for receiving reports
> from the host. SETUP/SET_REPORT method is not supported, and this causes
> a number of compatibility problems with various host drivers, especially
> in the case of keyboard emulation using f_hid.
>
>   - Some hosts do not support the OUT Endpoint and ignore it,
>     so it becomes impossible for the gadget to receive a report
>     from the host. In the case of a keyboard, the gadget loses
>     the ability to receive the status of the LEDs.
>
>   - Some BIOSes/UEFIs can't work with HID devices with the OUT Endpoint
>     at all. This may be due to their bugs or incomplete implementation
>     of the HID standard.
>     For example, absolutely all Apple UEFIs can't handle the OUT Endpoint
>     if it goes after IN Endpoint in the descriptor and require the reverse
>     order (OUT, IN) which is a violation of the standard.
>     Other hosts either do not initialize gadgets with a descriptor
>     containing the OUT Endpoint completely (like some HP and DELL BIOSes
>     and embedded firmwares like on KVM switches), or initialize them,
>     but will not poll the IN Endpoint.
>
> This patch adds configfs option no_out_endpoint=1 to disable
> the OUT Endpoint and allows f_hid to receive reports from the host
> via SETUP/SET_REPORT.
>
> Previously, there was such a feature in f_hid, but it was replaced
> by the OUT Endpoint [1] in the commit 99c515005857 ("usb: gadget: hidg:
> register OUT INT endpoint for SET_REPORT"). So this patch actually
> returns the removed functionality while making it optional.
> For backward compatibility reasons, the OUT Endpoint mode remains
> the default behaviour.
>
>   - The OUT Endpoint mode provides the report queue and reduces
>     USB overhead (eliminating SETUP routine) on transmitting a report
>     from the host.
>
>   - If the SETUP/SET_REPORT mode is used, there is no report queue,
>     so the userspace will only read last report. For classic HID devices
>     like keyboards this is not a problem, since it's intended to transmit
>     the status of the LEDs and only the last report is important.
>     This mode provides better compatibility with strange and buggy
>     host drivers.
>
> Both modes passed USBCV tests. Checking with the USB protocol analyzer
> also confirmed that everything is working as it should and the new mode
> ensures operability in all of the described cases.
>
> Signed-off-by: Maxim Devaev <mdevaev@xxxxxxxxx>
> Link: https://www.spinics.net/lists/linux-usb/msg65494.html [1]
> ---
>  drivers/usb/gadget/function/f_hid.c | 220 +++++++++++++++++++++++-----
>  drivers/usb/gadget/function/u_hid.h |   1 +
>  2 files changed, 188 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
> index bb476e121eae..ca0a7d9eaa34 100644
> --- a/drivers/usb/gadget/function/f_hid.c
> +++ b/drivers/usb/gadget/function/f_hid.c
> @@ -45,12 +45,25 @@ struct f_hidg {
>         unsigned short                  report_desc_length;
>         char                            *report_desc;
>         unsigned short                  report_length;
> +       /*
> +        * use_out_ep - if true, the OUT Endpoint (interrupt out method)
> +        *              will be used to receive reports from the host
> +        *              using functions with the "intout" suffix.
> +        *              Otherwise, the OUT Endpoint will not be configured
> +        *              and the SETUP/SET_REPORT method ("ssreport" suffix)
> +        *              will be used to receive reports.
> +        */
> +       bool                            use_out_ep;
>
>         /* recv report */
> -       struct list_head                completed_out_req;
>         spinlock_t                      read_spinlock;
>         wait_queue_head_t               read_queue;
> +       /* recv report - interrupt out only (use_out_ep == 1) */
> +       struct list_head                completed_out_req;
>         unsigned int                    qlen;
> +       /* recv report - setup set_report only (use_out_ep == 0) */
> +       char                            *set_report_buf;
> +       unsigned int                    set_report_length;
>
>         /* send report */
>         spinlock_t                      write_spinlock;
> @@ -79,7 +92,7 @@ static struct usb_interface_descriptor hidg_interface_desc = {
>         .bDescriptorType        = USB_DT_INTERFACE,
>         /* .bInterfaceNumber    = DYNAMIC */
>         .bAlternateSetting      = 0,
> -       .bNumEndpoints          = 2,
> +       /* .bNumEndpoints       = DYNAMIC (depends on use_out_ep) */
>         .bInterfaceClass        = USB_CLASS_HID,
>         /* .bInterfaceSubClass  = DYNAMIC */
>         /* .bInterfaceProtocol  = DYNAMIC */
> @@ -140,7 +153,7 @@ static struct usb_ss_ep_comp_descriptor hidg_ss_out_comp_desc = {
>         /* .wBytesPerInterval   = DYNAMIC */
>  };
>
> -static struct usb_descriptor_header *hidg_ss_descriptors[] = {
> +static struct usb_descriptor_header *hidg_ss_descriptors_intout[] = {
>         (struct usb_descriptor_header *)&hidg_interface_desc,
>         (struct usb_descriptor_header *)&hidg_desc,
>         (struct usb_descriptor_header *)&hidg_ss_in_ep_desc,
> @@ -150,6 +163,14 @@ static struct usb_descriptor_header *hidg_ss_descriptors[] = {
>         NULL,
>  };
>
> +static struct usb_descriptor_header *hidg_ss_descriptors_ssreport[] = {
> +       (struct usb_descriptor_header *)&hidg_interface_desc,
> +       (struct usb_descriptor_header *)&hidg_desc,
> +       (struct usb_descriptor_header *)&hidg_ss_in_ep_desc,
> +       (struct usb_descriptor_header *)&hidg_ss_in_comp_desc,
> +       NULL,
> +};
> +
>  /* High-Speed Support */
>
>  static struct usb_endpoint_descriptor hidg_hs_in_ep_desc = {
> @@ -176,7 +197,7 @@ static struct usb_endpoint_descriptor hidg_hs_out_ep_desc = {
>                                       */
>  };
>
> -static struct usb_descriptor_header *hidg_hs_descriptors[] = {
> +static struct usb_descriptor_header *hidg_hs_descriptors_intout[] = {
>         (struct usb_descriptor_header *)&hidg_interface_desc,
>         (struct usb_descriptor_header *)&hidg_desc,
>         (struct usb_descriptor_header *)&hidg_hs_in_ep_desc,
> @@ -184,6 +205,13 @@ static struct usb_descriptor_header *hidg_hs_descriptors[] = {
>         NULL,
>  };
>
> +static struct usb_descriptor_header *hidg_hs_descriptors_ssreport[] = {
> +       (struct usb_descriptor_header *)&hidg_interface_desc,
> +       (struct usb_descriptor_header *)&hidg_desc,
> +       (struct usb_descriptor_header *)&hidg_hs_in_ep_desc,
> +       NULL,
> +};
> +
>  /* Full-Speed Support */
>
>  static struct usb_endpoint_descriptor hidg_fs_in_ep_desc = {
> @@ -210,7 +238,7 @@ static struct usb_endpoint_descriptor hidg_fs_out_ep_desc = {
>                                        */
>  };
>
> -static struct usb_descriptor_header *hidg_fs_descriptors[] = {
> +static struct usb_descriptor_header *hidg_fs_descriptors_intout[] = {
>         (struct usb_descriptor_header *)&hidg_interface_desc,
>         (struct usb_descriptor_header *)&hidg_desc,
>         (struct usb_descriptor_header *)&hidg_fs_in_ep_desc,
> @@ -218,6 +246,13 @@ static struct usb_descriptor_header *hidg_fs_descriptors[] = {
>         NULL,
>  };
>
> +static struct usb_descriptor_header *hidg_fs_descriptors_ssreport[] = {
> +       (struct usb_descriptor_header *)&hidg_interface_desc,
> +       (struct usb_descriptor_header *)&hidg_desc,
> +       (struct usb_descriptor_header *)&hidg_fs_in_ep_desc,
> +       NULL,
> +};
> +
>  /*-------------------------------------------------------------------------*/
>  /*                                 Strings                                 */
>
> @@ -241,8 +276,8 @@ static struct usb_gadget_strings *ct_func_strings[] = {
>  /*-------------------------------------------------------------------------*/
>  /*                              Char Device                                */
>
> -static ssize_t f_hidg_read(struct file *file, char __user *buffer,
> -                       size_t count, loff_t *ptr)
> +static ssize_t f_hidg_intout_read(struct file *file, char __user *buffer,
> +                                 size_t count, loff_t *ptr)
>  {
>         struct f_hidg *hidg = file->private_data;
>         struct f_hidg_req_list *list;
> @@ -255,15 +290,15 @@ static ssize_t f_hidg_read(struct file *file, char __user *buffer,
>
>         spin_lock_irqsave(&hidg->read_spinlock, flags);
>
> -#define READ_COND (!list_empty(&hidg->completed_out_req))
> +#define READ_COND_INTOUT (!list_empty(&hidg->completed_out_req))
>
>         /* wait for at least one buffer to complete */
> -       while (!READ_COND) {
> +       while (!READ_COND_INTOUT) {
>                 spin_unlock_irqrestore(&hidg->read_spinlock, flags);
>                 if (file->f_flags & O_NONBLOCK)
>                         return -EAGAIN;
>
> -               if (wait_event_interruptible(hidg->read_queue, READ_COND))
> +               if (wait_event_interruptible(hidg->read_queue, READ_COND_INTOUT))
>                         return -ERESTARTSYS;
>
>                 spin_lock_irqsave(&hidg->read_spinlock, flags);
> @@ -313,6 +348,60 @@ static ssize_t f_hidg_read(struct file *file, char __user *buffer,
>         return count;
>  }
>
> +#define READ_COND_SSREPORT (hidg->set_report_buf != NULL)
> +
> +static ssize_t f_hidg_ssreport_read(struct file *file, char __user *buffer,
> +                                   size_t count, loff_t *ptr)
> +{
> +       struct f_hidg *hidg = file->private_data;
> +       char *tmp_buf = NULL;
> +       unsigned long flags;
> +
> +       if (!count)
> +               return 0;
> +
> +       spin_lock_irqsave(&hidg->read_spinlock, flags);
> +
> +       while (!READ_COND_SSREPORT) {
> +               spin_unlock_irqrestore(&hidg->read_spinlock, flags);
> +               if (file->f_flags & O_NONBLOCK)
> +                       return -EAGAIN;
> +
> +               if (wait_event_interruptible(hidg->read_queue, READ_COND_SSREPORT))
> +                       return -ERESTARTSYS;
> +
> +               spin_lock_irqsave(&hidg->read_spinlock, flags);
> +       }
> +
> +       count = min_t(unsigned int, count, hidg->set_report_length);
> +       tmp_buf = hidg->set_report_buf;
> +       hidg->set_report_buf = NULL;
> +
> +       spin_unlock_irqrestore(&hidg->read_spinlock, flags);
> +
> +       if (tmp_buf != NULL) {
> +               count -= copy_to_user(buffer, tmp_buf, count);
> +               kfree(tmp_buf);
> +       } else {
> +               count = -ENOMEM;
> +       }
> +
> +       wake_up(&hidg->read_queue);
> +
> +       return count;
> +}
> +
> +static ssize_t f_hidg_read(struct file *file, char __user *buffer,
> +                          size_t count, loff_t *ptr)
> +{
> +       struct f_hidg *hidg = file->private_data;
> +
> +       if (hidg->use_out_ep)
> +               return f_hidg_intout_read(file, buffer, count, ptr);
> +       else
> +               return f_hidg_ssreport_read(file, buffer, count, ptr);
> +}
> +
>  static void f_hidg_req_complete(struct usb_ep *ep, struct usb_request *req)
>  {
>         struct f_hidg *hidg = (struct f_hidg *)ep->driver_data;
> @@ -433,14 +522,20 @@ static __poll_t f_hidg_poll(struct file *file, poll_table *wait)
>         if (WRITE_COND)
>                 ret |= EPOLLOUT | EPOLLWRNORM;
>
> -       if (READ_COND)
> -               ret |= EPOLLIN | EPOLLRDNORM;
> +       if (hidg->use_out_ep) {
> +               if (READ_COND_INTOUT)
> +                       ret |= EPOLLIN | EPOLLRDNORM;
> +       } else {
> +               if (READ_COND_SSREPORT)
> +                       ret |= EPOLLIN | EPOLLRDNORM;
> +       }
>
>         return ret;
>  }
>
>  #undef WRITE_COND
> -#undef READ_COND
> +#undef READ_COND_SSREPORT
> +#undef READ_COND_INTOUT
>
>  static int f_hidg_release(struct inode *inode, struct file *fd)
>  {
> @@ -467,7 +562,7 @@ static inline struct usb_request *hidg_alloc_ep_req(struct usb_ep *ep,
>         return alloc_ep_req(ep, length);
>  }
>
> -static void hidg_set_report_complete(struct usb_ep *ep, struct usb_request *req)
> +static void hidg_intout_complete(struct usb_ep *ep, struct usb_request *req)
>  {
>         struct f_hidg *hidg = (struct f_hidg *) req->context;
>         struct usb_composite_dev *cdev = hidg->func.config->cdev;
> @@ -502,6 +597,37 @@ static void hidg_set_report_complete(struct usb_ep *ep, struct usb_request *req)
>         }
>  }
>
> +static void hidg_ssreport_complete(struct usb_ep *ep, struct usb_request *req)
> +{
> +       struct f_hidg *hidg = (struct f_hidg *)req->context;
> +       struct usb_composite_dev *cdev = hidg->func.config->cdev;
> +       char *new_buf = NULL;
> +       unsigned long flags;
> +
> +       if (req->status != 0 || req->buf == NULL || req->actual == 0) {
> +               ERROR(cdev,
> +                     "%s FAILED: status=%d, buf=%p, actual=%d\n",
> +                     __func__, req->status, req->buf, req->actual);
> +               return;
> +       }
> +
> +       spin_lock_irqsave(&hidg->read_spinlock, flags);
> +
> +       new_buf = krealloc(hidg->set_report_buf, req->actual, GFP_ATOMIC);
> +       if (new_buf == NULL) {
> +               spin_unlock_irqrestore(&hidg->read_spinlock, flags);
> +               return;
> +       }
> +       hidg->set_report_buf = new_buf;
> +
> +       hidg->set_report_length = req->actual;
> +       memcpy(hidg->set_report_buf, req->buf, req->actual);
> +
> +       spin_unlock_irqrestore(&hidg->read_spinlock, flags);
> +
> +       wake_up(&hidg->read_queue);
> +}
> +
>  static int hidg_setup(struct usb_function *f,
>                 const struct usb_ctrlrequest *ctrl)
>  {
> @@ -549,7 +675,11 @@ static int hidg_setup(struct usb_function *f,
>         case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8
>                   | HID_REQ_SET_REPORT):
>                 VDBG(cdev, "set_report | wLength=%d\n", ctrl->wLength);
> -               goto stall;
> +               if (hidg->use_out_ep)
> +                       goto stall;
> +               req->complete = hidg_ssreport_complete;
> +               req->context  = hidg;
> +               goto respond;
>                 break;
>
>         case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8
> @@ -637,15 +767,18 @@ static void hidg_disable(struct usb_function *f)
>         unsigned long flags;
>
>         usb_ep_disable(hidg->in_ep);
> -       usb_ep_disable(hidg->out_ep);
>
> -       spin_lock_irqsave(&hidg->read_spinlock, flags);
> -       list_for_each_entry_safe(list, next, &hidg->completed_out_req, list) {
> -               free_ep_req(hidg->out_ep, list->req);
> -               list_del(&list->list);
> -               kfree(list);
> +       if (hidg->out_ep) {
> +               usb_ep_disable(hidg->out_ep);
> +
> +               spin_lock_irqsave(&hidg->read_spinlock, flags);
> +               list_for_each_entry_safe(list, next, &hidg->completed_out_req, list) {
> +                       free_ep_req(hidg->out_ep, list->req);
> +                       list_del(&list->list);
> +                       kfree(list);
> +               }
> +               spin_unlock_irqrestore(&hidg->read_spinlock, flags);
>         }
> -       spin_unlock_irqrestore(&hidg->read_spinlock, flags);
>
>         spin_lock_irqsave(&hidg->write_spinlock, flags);
>         if (!hidg->write_pending) {
> @@ -691,8 +824,7 @@ static int hidg_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>                 }
>         }
>
> -
> -       if (hidg->out_ep != NULL) {
> +       if (hidg->use_out_ep && hidg->out_ep != NULL) {
>                 /* restart endpoint */
>                 usb_ep_disable(hidg->out_ep);
>
> @@ -717,7 +849,7 @@ static int hidg_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>                                         hidg_alloc_ep_req(hidg->out_ep,
>                                                           hidg->report_length);
>                         if (req) {
> -                               req->complete = hidg_set_report_complete;
> +                               req->complete = hidg_intout_complete;
>                                 req->context  = hidg;
>                                 status = usb_ep_queue(hidg->out_ep, req,
>                                                       GFP_ATOMIC);
> @@ -743,7 +875,8 @@ static int hidg_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>         }
>         return 0;
>  disable_out_ep:
> -       usb_ep_disable(hidg->out_ep);
> +       if (hidg->out_ep)
> +               usb_ep_disable(hidg->out_ep);
>  free_req_in:
>         if (req_in)
>                 free_ep_req(hidg->in_ep, req_in);
> @@ -795,14 +928,21 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
>                 goto fail;
>         hidg->in_ep = ep;
>
> -       ep = usb_ep_autoconfig(c->cdev->gadget, &hidg_fs_out_ep_desc);
> -       if (!ep)
> -               goto fail;
> -       hidg->out_ep = ep;
> +       hidg->out_ep = NULL;
> +       if (hidg->use_out_ep) {
> +               ep = usb_ep_autoconfig(c->cdev->gadget, &hidg_fs_out_ep_desc);
> +               if (!ep)
> +                       goto fail;
> +               hidg->out_ep = ep;
> +       }
> +
> +       /* used only if use_out_ep == 1 */
> +       hidg->set_report_buf = NULL;
>
>         /* set descriptor dynamic values */
>         hidg_interface_desc.bInterfaceSubClass = hidg->bInterfaceSubClass;
>         hidg_interface_desc.bInterfaceProtocol = hidg->bInterfaceProtocol;
> +       hidg_interface_desc.bNumEndpoints = hidg->use_out_ep ? 2 : 1;
>         hidg->protocol = HID_REPORT_PROTOCOL;
>         hidg->idle = 1;
>         hidg_ss_in_ep_desc.wMaxPacketSize = cpu_to_le16(hidg->report_length);
> @@ -833,9 +973,19 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
>         hidg_ss_out_ep_desc.bEndpointAddress =
>                 hidg_fs_out_ep_desc.bEndpointAddress;
>
> -       status = usb_assign_descriptors(f, hidg_fs_descriptors,
> -                       hidg_hs_descriptors, hidg_ss_descriptors,
> -                       hidg_ss_descriptors);
> +       if (hidg->use_out_ep)
> +               status = usb_assign_descriptors(f,
> +                       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;
>
> @@ -950,6 +1100,7 @@ CONFIGFS_ATTR(f_hid_opts_, name)
>
>  F_HID_OPT(subclass, 8, 255);
>  F_HID_OPT(protocol, 8, 255);
> +F_HID_OPT(no_out_endpoint, 8, 1);
>  F_HID_OPT(report_length, 16, 65535);
>
>  static ssize_t f_hid_opts_report_desc_show(struct config_item *item, char *page)
> @@ -1009,6 +1160,7 @@ CONFIGFS_ATTR_RO(f_hid_opts_, dev);
>  static struct configfs_attribute *hid_attrs[] = {
>         &f_hid_opts_attr_subclass,
>         &f_hid_opts_attr_protocol,
> +       &f_hid_opts_attr_no_out_endpoint,
>         &f_hid_opts_attr_report_length,
>         &f_hid_opts_attr_report_desc,
>         &f_hid_opts_attr_dev,
> @@ -1093,6 +1245,7 @@ static void hidg_free(struct usb_function *f)
>         hidg = func_to_hidg(f);
>         opts = container_of(f->fi, struct f_hid_opts, func_inst);
>         kfree(hidg->report_desc);
> +       kfree(hidg->set_report_buf);
>         kfree(hidg);
>         mutex_lock(&opts->lock);
>         --opts->refcnt;
> @@ -1139,6 +1292,7 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
>                         return ERR_PTR(-ENOMEM);
>                 }
>         }
> +       hidg->use_out_ep = !opts->no_out_endpoint;
>
>         mutex_unlock(&opts->lock);
>
> diff --git a/drivers/usb/gadget/function/u_hid.h b/drivers/usb/gadget/function/u_hid.h
> index 98d6af558c03..84bb70292855 100644
> --- a/drivers/usb/gadget/function/u_hid.h
> +++ b/drivers/usb/gadget/function/u_hid.h
> @@ -20,6 +20,7 @@ struct f_hid_opts {
>         int                             minor;
>         unsigned char                   subclass;
>         unsigned char                   protocol;
> +       unsigned char                   no_out_endpoint;
>         unsigned short                  report_length;
>         unsigned short                  report_desc_length;
>         unsigned char                   *report_desc;
> --
> 2.32.0

Reviewed-by: Maciej Żenczykowski <zenczykowski@xxxxxxxxx>