From: Peter Chen <peter.chen@freescale.com>
To: Daniel Mack <daniel@zonque.org>
Cc: <balbi@ti.com>, <linux-usb@vger.kernel.org>,
<andrzej.p@samsung.com>, <zonque@gmail.com>, <tiwai@suse.de>,
<stable@vger.kernel.org>, Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [PATCH 1/1] usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth
Date: Wed, 15 Jul 2015 08:23:43 +0800 [thread overview]
Message-ID: <20150715002341.GA30154@shlinux2> (raw)
In-Reply-To: <55A56B47.2090608@zonque.org>
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
prev parent reply other threads:[~2015-07-15 1:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-14 8:29 [PATCH 1/1] usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth Peter Chen
2015-07-14 20:04 ` Daniel Mack
2015-07-15 0:23 ` Peter Chen [this message]
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