Re: [PATCH v3 1/2] usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth

[Daniel Mack <daniel@zonque.org>]

On 07/27/2015 08:51 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>
> ---
> 
> 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 | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
> index 6d3eb8b..51ca32d 100644
> --- a/drivers/usb/gadget/function/f_uac2.c
> +++ b/drivers/usb/gadget/function/f_uac2.c
> @@ -987,6 +987,8 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
>  	struct f_uac2_opts *uac2_opts;
>  	struct usb_string *us;
>  	int ret;
> +	u16 max_packet_size;
> +	struct usb_endpoint_descriptor *ep_desc;
>  
>  	uac2_opts = container_of(fn->fi, struct f_uac2_opts, func_inst);
>  
> @@ -1070,10 +1072,37 @@ 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 */
> +	ep_desc = &fs_epin_desc;
> +	max_packet_size = num_channels(uac2_opts->p_chmask) *
> +		uac2_opts->p_ssize * DIV_ROUND_UP(uac2_opts->p_srate,
> +			1000 / (1 << (ep_desc->bInterval - 1)));
> +	ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size),
> +				ep_desc->wMaxPacketSize);
> +
> +	ep_desc = &fs_epout_desc;
> +	max_packet_size = num_channels(uac2_opts->c_chmask) *
> +		uac2_opts->c_ssize * DIV_ROUND_UP(uac2_opts->c_srate,
> +			1000 / (1 << (ep_desc->bInterval - 1)));
> +	ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size),
> +				ep_desc->wMaxPacketSize);
> +
> +	ep_desc = &hs_epin_desc;
> +	max_packet_size = num_channels(uac2_opts->p_chmask) *
> +		uac2_opts->p_ssize * DIV_ROUND_UP(uac2_opts->p_srate,
> +			8000 / (1 << (ep_desc->bInterval - 1)));
> +	ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size),
> +				ep_desc->wMaxPacketSize);
> +
> +	ep_desc = &hs_epout_desc;
> +	max_packet_size = num_channels(uac2_opts->c_chmask) *
> +		uac2_opts->c_ssize * DIV_ROUND_UP(uac2_opts->c_srate,
> +			8000 / (1 << (ep_desc->bInterval - 1)));
> +	ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size),
> +				ep_desc->wMaxPacketSize);

Basically, the same operation is repeated 4 times here. What about
factoring the code out to a helper function, so that the call site looks
like this:

  set_ep_max_packet_size(&fs_epin_desc,  uac2_opts, 1000);
  set_ep_max_packet_size(&fs_epout_desc, uac2_opts, 1000);
  set_ep_max_packet_size(&hs_epin_desc,  uac2_opts, 8000);
  set_ep_max_packet_size(&hs_epout_desc, uac2_opts, 8000);


Other than that, the patch now looks good to me!


Thanks,
Daniel



> +
>  	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)
>