linux-kernel - RE: [PATCH] usb: gadget: uvc: add bInterval checking for HS mode

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Date:   Mon, 8 Mar 2021 08:28:08 +0000
From:   Pawel Laszczak <pawell@...ence.com>
To:     Peter Chen <hzpeterchen@...il.com>
CC:     "balbi@...nel.org" <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB list <linux-usb@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>
Subject: RE: [PATCH] usb: gadget: uvc: add bInterval checking for HS mode

>
>On Fri, Mar 5, 2021 at 12:40 AM Pawel Laszczak <mailto:pawell@...ence.com> wrote:
>From: Pawel Laszczak <mailto:pawell@...ence.com>
>
>Patch adds extra checking for bInterval passed by configfs.
>The 5.6.4 chapter of USB Specification (rev. 2.0) say:
>"A high-bandwidth endpoint must specify a period of 1x125 µs
>(i.e., a bInterval value of 1)."
>
>The issue was observed during testing UVC class on CV.
>I treat this change as improvement because we can control
>bInterval by configfs.
>
>Signed-off-by: Pawel Laszczak <mailto:pawell@...ence.com>
>---
> drivers/usb/gadget/function/f_uvc.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
>diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
>index 44b4352a2676..5d62720bb9e1 100644
>--- a/drivers/usb/gadget/function/f_uvc.c
>+++ b/drivers/usb/gadget/function/f_uvc.c
>@@ -631,6 +631,12 @@ uvc_function_bind(struct usb_configuration *c, struct usb_function *f)
>                cpu_to_le16(min(opts->streaming_maxpacket, 1023U));
>        uvc_fs_streaming_ep.bInterval = opts->streaming_interval;
>
>+       /* A high-bandwidth endpoint must specify a bInterval value of 1 */
>+       if (max_packet_mult > 1)
>+               uvc_hs_streaming_ep.bInterval = 1;
>+       else
>+               uvc_hs_streaming_ep.bInterval = opts->streaming_interval;
>+
>
>There is a "uvc_hs_streaming_ep.bInterval = opts->streaming_interval;" again at below code
>Besides, the default value is 1 for opts->streaming_interval. What the real issue you observed
>at CV test?
>

The issue occurs when I intentionally set:
        echo 3072  > functions/$FUNCTION/streaming_maxpacket
        echo 4 > functions/$FUNCTION/streaming_interval

Then for  CV CH9 TD 9.5: Endpoint Descriptor test it got:
"(Mult = 2)Illegal high speed isochronous endpoint MaxPacketSize : 0x400
(USB: 1.2.78) A High speed Interrupt/Isochronous endpoint must have a MaxPacketSize between
683 and 1024 and bInterval value of 1 when the Mult value is two."

For default value CV passed.  Of course, I can fix it by changing  streaming_interval, but I thought that
it could be good to have protection against this issue. 
Especially since Usb 2 specification say that bInterval must be 1 for high bandwidth endpoints.

Pawel

>Peter
>
>        uvc_hs_streaming_ep.wMaxPacketSize =
>                cpu_to_le16(max_packet_size | ((max_packet_mult - 1) << 11));
>        uvc_hs_streaming_ep.bInterval = opts->streaming_interval;
>--
>2.25.1