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ALSA: usb-audio: Fix max bytes-per-interval calculation 

The maxpacksize field in struct audioformat represents the maximum number
of bytes per isochronous interval. The current implementation only
special-cases high-speed endpoints and does not account for the different
computations required for SuperSpeed, SuperSpeedPlus, or eUSB2. As a
result, USB audio class devices operating at these speeds may fail to
stream correctly. The issue was observed on a MOTU 16A (2025) interface,
which requires more than 1024 bytes per interval at SuperSpeed.

This patch replaces the existing logic with a helper that computes the
correct maximum bytes-per-interval for all USB speeds, borrowing the logic
used in drivers/usb/core/urb.c.

Signed-off-by: Dylan Robinson <dylan_robinson@motu.com>
Link: https://patch.msgid.link/20251124210518.90054-1-dylan_robinson@motu.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Dylan Robinson 2025-11-24 16:05:18 -05:00 committed by Takashi Iwai
parent 9ef1203fc7
commit a748e1dbb2
1 changed files with 32 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
sound/usb/stream.c
View File

@ -684,6 +684,37 @@ snd_usb_find_output_terminal_descriptor(struct usb_host_interface *ctrl_iface,
return NULL;
}
static unsigned int
snd_usb_max_bytes_per_interval(struct snd_usb_audio *chip,
struct usb_host_interface *alts)
{
struct usb_host_endpoint *ep = &alts->endpoint[0];
unsigned int max_bytes = usb_endpoint_maxp(&ep->desc);
/* SuperSpeed isoc endpoints have up to 16 bursts of up to 3 packets each */
if (snd_usb_get_speed(chip->dev) >= USB_SPEED_SUPER) {
int burst = 1 + ep->ss_ep_comp.bMaxBurst;
int mult = USB_SS_MULT(ep->ss_ep_comp.bmAttributes);
max_bytes *= burst;
max_bytes *= mult;
}
if (snd_usb_get_speed(chip->dev) == USB_SPEED_SUPER_PLUS &&
USB_SS_SSP_ISOC_COMP(ep->ss_ep_comp.bmAttributes)) {
max_bytes = le32_to_cpu(ep->ssp_isoc_ep_comp.dwBytesPerInterval);
}
/* High speed, 1-3 packets/uframe, max 6 for eUSB2 double bw */
if (snd_usb_get_speed(chip->dev) == USB_SPEED_HIGH) {
if (usb_endpoint_is_hs_isoc_double(chip->dev, ep))
max_bytes = le32_to_cpu(ep->eusb2_isoc_ep_comp.dwBytesPerInterval);
else
max_bytes *= usb_endpoint_maxp_mult(&ep->desc);
}
return max_bytes;
}
static struct audioformat *
audio_format_alloc_init(struct snd_usb_audio *chip,
struct usb_host_interface *alts,
@ -703,11 +734,8 @@ audio_format_alloc_init(struct snd_usb_audio *chip,
fp->ep_attr = get_endpoint(alts, 0)->bmAttributes;
fp->datainterval = snd_usb_parse_datainterval(chip, alts);
fp->protocol = protocol;
fp->maxpacksize = le16_to_cpu(get_endpoint(alts, 0)->wMaxPacketSize);
fp->maxpacksize = snd_usb_max_bytes_per_interval(chip, alts);
fp->channels = num_channels;
if (snd_usb_get_speed(chip->dev) == USB_SPEED_HIGH)
fp->maxpacksize = (((fp->maxpacksize >> 11) & 3) + 1)
* (fp->maxpacksize & 0x7ff);
fp->clock = clock;
INIT_LIST_HEAD(&fp->list);