Re: [PATCHv2 8/9] hackrf: add support for transmitter

Hans Verkuil
2015-07-27T20:38:48Z

On 07/27/2015 10:21 PM, Antti Palosaari wrote:
> On 07/17/2015 05:43 PM, Hans Verkuil wrote:
>> On 07/16/2015 09:04 AM, Antti Palosaari wrote:
>>> HackRF SDR device has both receiver and transmitter. There is limitation
>>> that receiver and transmitter cannot be used at the same time
>>> (half-duplex operation). That patch implements transmitter support to
>>> existing receiver only driver.
>>>
>>> Cc: Hans Verkuil <hverkuil@xs4all.nl>
>>> Signed-off-by: Antti Palosaari <crope@iki.fi>
>>> ---
>>> drivers/media/usb/hackrf/hackrf.c | 787 +++++++++++++++++++++++++++-----------
>>> 1 file changed, 572 insertions(+), 215 deletions(-)
>>>
>>
>>
>>> @@ -611,8 +751,15 @@ static int hackrf_queue_setup(struct vb2_queue *vq,
>>> unsigned int *nplanes, unsigned int sizes[], void *alloc_ctxs[])
>>> {
>>> struct hackrf_dev *dev = vb2_get_drv_priv(vq);
>>> + struct usb_interface *intf = dev->intf;
>>> + int ret;
>>>
>>> - dev_dbg(dev->dev, "nbuffers=%d\n", *nbuffers);
>>> + dev_dbg(&intf->dev, "nbuffers=%d\n", *nbuffers);
>>> +
>>> + if (test_and_set_bit(QUEUE_SETUP, &dev->flags)) {
>>> + ret = -EBUSY;
>>> + goto err;
>>> + }
>>
>> This doesn't work. The bit is only cleared when start_streaming fails or
>> stop_streaming is called. But the application can also call REQBUFS again
>> or just close the file handle, and then QUEUE_SETUP should also be cleared.
>>
>> But why is this here in the first place? It doesn't seem to do anything
>> useful (except mess up the v4l2-compliance tests).
>>
>> I've removed it and it now seems to work OK.
>
> It is there to block simultaneous use of receiver and transmitter.
> Device could operate only single mode at the time - receiving or
> transmitting. Driver shares streaming buffers.
>
> Any idea how I can easily implement correct blocking?

Since each video_device struct has its own vb2_queue I wouldn't put the check
here. Instead, put the check in the start_streaming callback. And the check
is easy enough: if you want to start capturing, then call
vb2_is_streaming(&tx_vb2_queue). If you want to start output, then call
vb2_is_streaming(&rx_vb2_queue). If the other 'side' is streaming, then
return EBUSY.

It's perfectly valid to allocate the buffers, but actually streaming is an
exclusive operation.

Regards,

Hans