Re: [PATCH v5 1/1] usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth

[Daniel Mack <daniel@zonque.org>]

On 07/28/2015 11:17 AM, Peter Chen wrote:
> According to USB Audio Device 2.0 Spec, Ch4.10.1.1:
> wMaxPacketSize is defined as follows:
> Maximum packet size this endpoint is capable of sending or receiving
> when this configuration is selected.
> This is determined by the audio bandwidth constraints of the endpoint.
> 
> In current code, the wMaxPacketSize is defined as the maximum packet size
> for ISO endpoint, and it will let the host reserve much more space than
> it really needs, so that we can't let more endpoints work together at
> one frame.
> 
> We find this issue when we try to let 4 f_uac2 gadgets work together [1]
> at FS connection.
> 
> [1]http://www.spinics.net/lists/linux-usb/msg123478.html
> 
> Cc: andrzej.p@samsung.com
> Cc: Daniel Mack <zonque@gmail.com>
> Cc: tiwai@suse.de
> Cc: <stable@vger.kernel.org> #v3.18+
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Signed-off-by: Peter Chen <peter.chen@freescale.com>

Looks good to me now! I currently don't have hardware to test this on,
though.

  Acked-by: Daniel Mack <zonque@gmail.com>


Thanks,
Daniel

> ---
> 
> Changes for v5:
> - Add additional parameters 'is_playback' for helper
> - Add const for parameter 'struct f_uac2_opts *uac2_opts'
> - Put all three int variables at one line 
> - Fix the CodeStyle problem
> 
> Changes for v4:
> - Add helper set_ep_max_packet_size to calculate max packet size
> 
> Changes for v3:
> - Consider 'bInterval' to calculate wMaxPacketSize
> - playback endpoint is IN ep, and capture endpoint is OUT ep
> 
> Changes for v2:
> - Using DIV_ROUND_UP to calculate max packet size
> 
>  drivers/usb/gadget/function/f_uac2.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
> index 5318615..fa93d79 100644
> --- a/drivers/usb/gadget/function/f_uac2.c
> +++ b/drivers/usb/gadget/function/f_uac2.c
> @@ -975,6 +975,29 @@ free_ep(struct uac2_rtd_params *prm, struct usb_ep *ep)
>  			"%s:%d Error!\n", __func__, __LINE__);
>  }
>  
> +static void set_ep_max_packet_size(const struct f_uac2_opts *uac2_opts,
> +	struct usb_endpoint_descriptor *ep_desc,
> +	unsigned int factor, bool is_playback)
> +{
> +	int chmask, srate, ssize;
> +	u16 max_packet_size;
> +
> +	if (is_playback) {
> +		chmask = uac2_opts->p_chmask;
> +		srate = uac2_opts->p_srate;
> +		ssize = uac2_opts->p_ssize;
> +	} else {
> +		chmask = uac2_opts->c_chmask;
> +		srate = uac2_opts->c_srate;
> +		ssize = uac2_opts->c_ssize;
> +	}
> +
> +	max_packet_size = num_channels(chmask) * ssize *
> +		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
> +	ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size),
> +				ep_desc->wMaxPacketSize);
> +}
> +
>  static int
>  afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
>  {
> @@ -1070,10 +1093,14 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
>  	uac2->p_prm.uac2 = uac2;
>  	uac2->c_prm.uac2 = uac2;
>  
> +	/* Calculate wMaxPacketSize according to audio bandwidth */
> +	set_ep_max_packet_size(uac2_opts, &fs_epin_desc, 1000, true);
> +	set_ep_max_packet_size(uac2_opts, &fs_epout_desc, 1000, false);
> +	set_ep_max_packet_size(uac2_opts, &hs_epin_desc, 8000, true);
> +	set_ep_max_packet_size(uac2_opts, &hs_epout_desc, 8000, false);
> +
>  	hs_epout_desc.bEndpointAddress = fs_epout_desc.bEndpointAddress;
> -	hs_epout_desc.wMaxPacketSize = fs_epout_desc.wMaxPacketSize;
>  	hs_epin_desc.bEndpointAddress = fs_epin_desc.bEndpointAddress;
> -	hs_epin_desc.wMaxPacketSize = fs_epin_desc.wMaxPacketSize;
>  
>  	ret = usb_assign_descriptors(fn, fs_audio_desc, hs_audio_desc, NULL);
>  	if (ret)
>