From: Daniel Mack <daniel@zonque.org>
To: Peter Chen <peter.chen@freescale.com>, balbi@ti.com
Cc: 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: Tue, 14 Jul 2015 16:04:23 -0400 [thread overview]
Message-ID: <55A56B47.2090608@zonque.org> (raw)
In-Reply-To: <1436862578-31625-1-git-send-email-peter.chen@freescale.com>
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?
> + 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().
> + 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.
Thanks,
Daniel
next prev parent reply other threads:[~2015-07-14 20:04 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 [this message]
2015-07-15 0:23 ` Peter Chen
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