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

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Date:   Mon, 8 Mar 2021 12:59:15 +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

Peter,

You're right. This patch is wrong. I didn't remove the "uvc_hs_streaming_ep.bInterval"
assignment. 

It has been fixed in v2.

Pawel

>>
>>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

Thanks,
Pawel Laszczak