Re: [alsa-devel] [PATCH 4/9 v2] ALSA: usb-audio: use usb_fill_int_urb()

20 Jun 2018

On Wed, 20 Jun 2018 11:38:27 +0200,
Sebastian Andrzej Siewior wrote:
...
Using usb_fill_int_urb() helps to find code which initializes an
URB. A grep for members of the struct (like ->complete) reveal lots
of other things, too.
data_ep_set_params() additionally sets urb->transfer_buffer_length which
was not the case earlier.
usb_fill_int_urb() ensures that syncinterval is within the allowed range
on HS/SS. The interval value seems to come from
snd_usb_parse_datainterval() which is bInterval - 1 and only in the rage
1 … 4. So in order to keep the magic working I pass datainterval + 1.
This needs more explanation.  By this conversion, the interval
computation becomes really tricky.
There are two interval calculations.  The first one is
fp->datainterval and it's from snd_usb_parse_datainterval() as you
mentioned.  And a tricky part is that fp->datainterval is 0 on
FULL_SPEED.  Casually, fp->datainterval+1 will be translated to the
correct value since (0 + 1) == (1 << 0).
OTOH, for the sync EP, it's taken from ep->syncinterval, which is set
in snd_usb_add_endpoint().  Luckily, again, ep->syncinterval + 1 works
for FULL_SPEED as well, as (1 + 1) == (1 << 1).
thanks,
Takashi
...
Cc: Jaroslav Kysela perex@perex.cz
Cc: Takashi Iwai tiwai@suse.com
Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de

v1…v2: description changes (spelling + usb_fill_int_urb() ensures
       "syncinterval" not data_ep_set_params())
sound/usb/endpoint.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index c90607ebe155..bbc02db5b417 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -772,6 +772,8 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
   /* allocate and initialize data urbs */
   for (i = 0; i < ep->nurbs; i++) {
   	struct snd_urb_ctx *u = &ep->urb[i];

void *buf;


u->index = i;
  u->ep = ep;
  u->packets = urb_packs;

@@ -783,16 +785,13 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
   	if (!u->urb)
   		goto out_of_memory;

u->urb->transfer_buffer =


	usb_alloc_coherent(ep->chip->dev, u->buffer_size,


			   GFP_KERNEL, &u->urb->transfer_dma);


if (!u->urb->transfer_buffer)




buf = usb_alloc_coherent(ep->chip->dev, u->buffer_size,


			 GFP_KERNEL, &u->urb->transfer_dma);


if (!buf)
goto out_of_memory;




u->urb->pipe = ep->pipe;




usb_fill_int_urb(u->urb, NULL, ep->pipe, buf, u->buffer_size,


		 snd_complete_urb, u, ep->datainterval + 1);

u->urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;


u->urb->interval = 1 << ep->datainterval;


u->urb->context = u;


u->urb->complete = snd_complete_urb;

INIT_LIST_HEAD(&u->ready_list);
}

@@ -823,15 +822,12 @@ static int sync_ep_set_params(struct snd_usb_endpoint *ep)
   	u->urb = usb_alloc_urb(1, GFP_KERNEL);
   	if (!u->urb)
   		goto out_of_memory;

u->urb->transfer_buffer = ep->syncbuf + i * 4;




usb_fill_int_urb(u->urb, NULL, ep->pipe, ep->syncbuf + i * 4, 4,


		 snd_complete_urb, u, ep->syncinterval + 1);


u->urb->transfer_dma = ep->sync_dma + i * 4;


u->urb->transfer_buffer_length = 4;


u->urb->pipe = ep->pipe;

u->urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;
u->urb->number_of_packets = 1;

u->urb->interval = 1 << ep->syncinterval;


u->urb->context = u;


u->urb->complete = snd_complete_urb;

}
ep->nurbs = SYNC_URBS;


-- 
2.17.1

    