On 09/01/2015 02:42 AM, Clemens Ladisch wrote: > Shuah Khan wrote: >> +++ b/sound/usb/stream.c >> pcm->private_data = as; >> pcm->private_free = snd_usb_audio_pcm_free; >> pcm->info_flags = 0; >> + pcm->nonatomic = true; > > Why do you think you need nonatomic mode in the USB audio driver? > Short answer is that the need is not a generic one, but a device specific need to add a fewature. Now the longer version below. This is for a for AU0828 Hauppauge HVR950Q media device. snd-usb-audio driver provides Audio Capture support on this device with DVB and Video drivers driving the device for Digital and Video functions. I have been working on adding Media Controller support for this chip as chip specific feature in ALSA. This will allow sharing resources such as the tuner across the drivers that control the device (DVB, Video, snd-usb-audio). Media Controller framework uses a mutex to protect access to resources, hence there is a need to hold this mutex from SNDRV_PCM_TRIGGER_START and SNDRV_PCM_TRIGGER_STOP which could run in IRQ context. The Media Controller mutex can't be converted to a spinlock as it would break I2C drivers. During review, the idea to run PCM in non-atomic mode came up as a way to solve the problem. The actual solution would run PCM in nonatomic context only for the AU0828 Hauppauge HVR950Q chip. The above change is a quick try to see if PCM nonatomic works with this device. I have to figure out another way to solve the problem as this isn't an option. Hope this helps answer your question. If you would like more information on the ALSA Media Controller work for this device, I can provide links to the previous patch series. thanks, -- Shuah -- Shuah Khan Sr. Linux Kernel Developer Open Source Innovation Group Samsung Research America (Silicon Valley) shuahkh@xxxxxxxxxxxxxxx | (970) 217-8978 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
