Re: [PATCH v2 1/1] usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth

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

On Wed, Jul 22, 2015 at 10:04:30AM +0200, Daniel Mack wrote:
> On 07/22/2015 08:45 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: 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 v2:
> > - Using DIV_ROUND_UP to calculate max packet size
> > 
> >  drivers/usb/gadget/function/f_uac2.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
> > index 6d3eb8b..6eaa4c4 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 +1071,19 @@ 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
> > +		* DIV_ROUND_UP(uac2_opts->c_srate, 1000);
> > +	p_max_packet_size = uac2_opts->p_chmask * uac2_opts->p_ssize
> > +		* DIV_ROUND_UP(uac2_opts->p_srate, 1000);
> > +	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;
> > +	}
> > +	fs_epin_desc.wMaxPacketSize = cpu_to_le16(c_max_packet_size);
> > +	fs_epout_desc.wMaxPacketSize = cpu_to_le16(p_max_packet_size);
> > +
> >  	hs_epout_desc.bEndpointAddress = fs_epout_desc.bEndpointAddress;
> >  	hs_epout_desc.wMaxPacketSize = fs_epout_desc.wMaxPacketSize;
> 
> Your calculation still doesn't take into account the endpoint's
> 'bInterval', and for HS, the value is still wrong.
> 
> 

You mean I need to consider high bandwidth ISO transfer (3 packets per
SoF)? 

-- 

Best Regards,
Peter Chen