linux-kernel - Re: [PATCH] usb: gadget: uvc:change the UVC_NUM

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Message-ID: <2afb9306-b957-9f60-f103-e1d5912e0218@codeaurora.org>
Date:   Tue, 26 Dec 2017 10:30:33 +0530
From:   Manu Gautam <mgautam@...eaurora.org>
To:     Lipengcheng <lpc.li@...ilicon.com>,
        "balbi@...nel.org" <balbi@...nel.org>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: uvc:change the UVC_NUM_REQUESTS value

Hi,


On 12/26/2017 8:22 AM, Lipengcheng wrote:
> The value is 4, it can cache four descriptors. When streaming_interval = 1,
> it can tolerate 500us. Some busy scenes, it may be more than 500us because
> cpu scheduling is not timely. There will have some problems. It is better
> set to eight.
>
> Signed-off-by: Pengcheng Li <lpc.li@...ilicon.com>
> ---
>  drivers/usb/gadget/function/uvc.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
> index a64e07e..901487e 100644
> --- a/drivers/usb/gadget/function/uvc.h
> +++ b/drivers/usb/gadget/function/uvc.h
> @@ -90,7 +90,7 @@ extern unsigned int uvc_gadget_trace_param;
>   * Driver specific constants
>   */
>
> -#define UVC_NUM_REQUESTS           4
> +#define UVC_NUM_REQUESTS           8

Can we rather make it 16?
I ran into similar issue on QCOM platform with DWC3 and with 8 requests also data loss
was observed. 16 requests (i.e. ~2msec) worked fine.

>  #define UVC_MAX_REQUEST_SIZE           64
>  #define UVC_MAX_EVENTS             4
>
> --
> 2.7.4
>
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