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

[Peter Chen <peter.chen@freescale.com>]

On Tue, Jul 14, 2015 at 04:04:23PM -0400, Daniel Mack wrote:
> Hi,
> 
> On 07/14/2015 04:29 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.
> 
> ...
> 
> > diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
> > index 6d3eb8b..0ed6f0e 100644
> > --- a/drivers/usb/gadget/function/f_uac2.c
> > +++ b/drivers/usb/gadget/function/f_uac2.c
> > @@ -987,6 +987,7 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
> >  	struct f_uac2_opts *uac2_opts;
> >  	struct usb_string *us;
> >  	int ret;
> > +	u16 c_max_packet_size, p_max_packet_size;
> >  
> >  	uac2_opts = container_of(fn->fi, struct f_uac2_opts, func_inst);
> >  
> > @@ -1070,6 +1071,29 @@ 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 */
> > +	c_max_packet_size = uac2_opts->c_chmask * uac2_opts->c_ssize
> > +		* uac2_opts->c_srate / 1000;
> > +	p_max_packet_size = uac2_opts->p_chmask * uac2_opts->p_ssize
> > +		* uac2_opts->p_srate / 1000;
> 
> For high-speed endpoints, we in fact have 8 microframes per frame, and
> the factor also depends on the endpoint's polling interval. See what
> afunc_set_alt() does here.
> 
> Did you test this in HS or FS setups or both?

It only has problem at FS setup.

> 
> > +	if ((c_max_packet_size > fs_epout_desc.wMaxPacketSize) ||
> > +		(p_max_packet_size > fs_epin_desc.wMaxPacketSize)) {
> > +		dev_err(dev, "parameters are incorrect\n");
> > +		goto err;
> > +	}
> > +	/*
> > +	 * Keep max packet size is multiplier of 4, and
> > +	 * a little larger than bandwidth.
> > +	 * Eg, for frame rate 44100, 1 channel, and 16 bits data
> > +	 * we need to reserve more than 44 * 2 bytes.
> > +	 */
> > +	c_max_packet_size +=  (4 - (c_max_packet_size % 4));
> 
> I guess DIV_ROUND_UP() allows you to account for the packets that are
> sent when the devision residue accumulator overflows. See
> agdev_iso_complete().

Thanks, I will check it.

> 
> > +	fs_epin_desc.wMaxPacketSize = min(cpu_to_le16(c_max_packet_size),
> > +		fs_epin_desc.wMaxPacketSize);
> > +	p_max_packet_size +=  (4 - (p_max_packet_size % 4));
> > +	fs_epout_desc.wMaxPacketSize = min(cpu_to_le16(p_max_packet_size),
> > +		fs_epout_desc.wMaxPacketSize);
> > +
> >  	hs_epout_desc.bEndpointAddress = fs_epout_desc.bEndpointAddress;
> >  	hs_epout_desc.wMaxPacketSize = fs_epout_desc.wMaxPacketSize;
> 
> We probably have to pass different values for the two settings, as they
> can't be the same once they contain pre-calculated values.
> 
> 

You mean we may have different wMaxPacketSize value for FS and HS?
Current f_uac2 does not support it, it only one group parameter
for packet size.

-- 

Best Regards,
Peter Chen