ALSA: usb-audio: Limit retrying sample rate reads

There are many USB audio devices with buggy firmware that don't react
with the sample rate reading properly.  This often results in the
flood of error messages and slowing down the operation.

The sample rate read back is basically only for confirming the sample
rate setup, and it's not critically important.  As a compromise, in
this patch, we stop the sample rate read back once when the device
gives errors more than tolerance (twice, as of now).  This should
improve most of error cases while we still can catch the firmware
bugginess.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/clock.c b/sound/usb/clock.c
index 7ccbcaf6a1476423e0d2becf0bf91f3463a47b46..26dd5f20f1494320735b47f60be79eab70b6e111 100644 (file)
--- a/sound/usb/clock.c
+++ b/sound/usb/clock.c
@@ -309,6 +309,9 @@ static int set_sample_rate_v1(struct snd_usb_audio *chip, int iface,
         * support reading */
        if (snd_usb_get_sample_rate_quirk(chip))
                return 0;
+       /* the firmware is likely buggy, don't repeat to fail too many times */
+       if (chip->sample_rate_read_error > 2)
+               return 0;
 
        if ((err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), UAC_GET_CUR,
                                   USB_TYPE_CLASS | USB_RECIP_ENDPOINT | USB_DIR_IN,
@@ -316,6 +319,7 @@ static int set_sample_rate_v1(struct snd_usb_audio *chip, int iface,
                                   data, sizeof(data))) < 0) {
                dev_err(&dev->dev, "%d:%d: cannot get freq at ep %#x\n",
                        iface, fmt->altsetting, ep);
+               chip->sample_rate_read_error++;
                return 0; /* some devices don't support reading */
        }
 

diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index a161c7c1b126651c558b0140678ad0d1e6f432d8..89b6853030de59e715482ba781dca4016a054bc5 100644 (file)
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -50,6 +50,7 @@ struct snd_usb_audio {
        
        int num_interfaces;
        int num_suspended_intf;
+       int sample_rate_read_error;
 
        struct list_head pcm_list;      /* list of pcm streams */
        struct list_head ep_list;       /* list of audio-related endpoints */