Apologies, forgot to note this patch requires:
https://patchwork.kernel.org/patch/10492053/
On 2018-06-27 14:41, Brad Love wrote:
> Addresses the following, which introduced a regression itself:
>
> Commit 509f89652f83 ("media: em28xx: fix a regression with HVR-950")
>
> The regression fix breaks dual transport stream support. When a
> tuner starts streaming it sets alt mode on the USB interface.
> The problem is both tuners share the same USB interface, so when
> the second tuner becomes active and sets alt mode on the interface
> it kills streaming on the other port.
>
> It was suggested to add a refcounter and only set alt mode if no
> tuners are currently active on the interface. This requires
> sharing some state amongst both tuner devices, with appropriate
> locking.
>
> What I've done here is the following:
> - Add a usage_count pointer to struct em28xx
> - Share usage_count between both em28xx devices
> - Only set alt mode if usage_count is zero
> - Increment usage_count when each tuner becomes active
> - Decrement usage_count when a tuner becomes idle
>
> With usage_count in the main em28xx struct, locking is handled as
> follows:
> - if a secondary tuner exists, lock dev->dev_next->lock
> - if no secondary tuner exists, lock dev->lock
>
> By using the above scheme a single tuner device, will lock itself,
> the first tuner in a dual tuner device will lock the second tuner,
> and the second tuner in a dual tuner device will lock itself aka
> the second tuner instance.
>
> Signed-off-by: Brad Love <b...@nextdimension.cc>
> ---
> drivers/media/usb/em28xx/em28xx-cards.c | 6 ++++-
> drivers/media/usb/em28xx/em28xx-dvb.c | 47
> +++++++++++++++++++++++++++++++--
> drivers/media/usb/em28xx/em28xx.h | 1 +
> 3 files changed, 51 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c
> b/drivers/media/usb/em28xx/em28xx-cards.c
> index 48bc505..91f9787 100644
> --- a/drivers/media/usb/em28xx/em28xx-cards.c
> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
> @@ -3374,8 +3374,10 @@ void em28xx_free_device(struct kref *ref)
> if (!dev->disconnected)
> em28xx_release_resources(dev);
>
> - if (dev->ts == PRIMARY_TS)
> + if (dev->ts == PRIMARY_TS) {
> kfree(dev->alt_max_pkt_size_isoc);
> + kfree(dev->usage_count);
> + }
>
> kfree(dev);
> }
> @@ -3793,6 +3795,8 @@ static int em28xx_usb_probe(struct usb_interface *intf,
> dev->is_audio_only = has_vendor_audio && !(has_video || has_dvb);
> dev->has_video = has_video;
> dev->ifnum = ifnum;
> + dev->usage_count = kcalloc(1, sizeof(unsigned int), GFP_KERNEL);
> + *dev->usage_count = 0;
>
> dev->ts = PRIMARY_TS;
> snprintf(dev->name, 28, "em28xx");
> diff --git a/drivers/media/usb/em28xx/em28xx-dvb.c
> b/drivers/media/usb/em28xx/em28xx-dvb.c
> index b778d8a..3a67831 100644
> --- a/drivers/media/usb/em28xx/em28xx-dvb.c
> +++ b/drivers/media/usb/em28xx/em28xx-dvb.c
> @@ -218,7 +218,19 @@ static int em28xx_start_streaming(struct em28xx_dvb *dvb)
> dvb_alt = dev->dvb_alt_isoc;
> }
>
> - usb_set_interface(udev, dev->ifnum, dvb_alt);
> + if (dev->dev_next)
> + mutex_lock(&dev->dev_next->lock);
> + else
> + mutex_lock(&dev->lock);
> +
> + if (*dev->usage_count == 0)
> + usb_set_interface(udev, dev->ifnum, dvb_alt);
> +
> + if (dev->dev_next)
> + mutex_unlock(&dev->dev_next->lock);
> + else
> + mutex_unlock(&dev->lock);
> +
> rc = em28xx_set_mode(dev, EM28XX_DIGITAL_MODE);
> if (rc < 0)
> return rc;
> @@ -250,6 +262,8 @@ static int em28xx_start_feed(struct dvb_demux_feed *feed)
> {
> struct dvb_demux *demux = feed->demux;
> struct em28xx_dvb *dvb = demux->priv;
> + struct em28xx_i2c_bus *i2c_bus = dvb->adapter.priv;
> + struct em28xx *dev = i2c_bus->dev;
> int rc, ret;
>
> if (!demux->dmx.frontend)
> @@ -263,6 +277,19 @@ static int em28xx_start_feed(struct dvb_demux_feed *feed)
> ret = em28xx_start_streaming(dvb);
> if (ret < 0)
> rc = ret;
> + else {
> + if (dev->dev_next)
> + mutex_lock(&dev->dev_next->lock);
> + else
> + mutex_lock(&dev->lock);
> +
> + *dev->usage_count = *dev->usage_count + 1;
> +
> + if (dev->dev_next)
> + mutex_unlock(&dev->dev_next->lock);
> + else
> + mutex_unlock(&dev->lock);
> + }
> }
>
> mutex_unlock(&dvb->lock);
> @@ -273,14 +300,30 @@ static int em28xx_stop_feed(struct dvb_demux_feed *feed)
> {
> struct dvb_demux *demux = feed->demux;
> struct em28xx_dvb *dvb = demux->priv;
> + struct em28xx_i2c_bus *i2c_bus = dvb->adapter.priv;
> + struct em28xx *dev = i2c_bus->dev;
> int err = 0;
>
> mutex_lock(&dvb->lock);
> dvb->nfeeds--;
>
> - if (!dvb->nfeeds)
> + if (!dvb->nfeeds) {
> err = em28xx_stop_streaming(dvb);
>
> + if (dev->dev_next)
> + mutex_lock(&dev->dev_next->lock);
> + else
> + mutex_lock(&dev->lock);
> +
> + *dev->usage_count = *dev->usage_count - 1;
> +
> + if (dev->dev_next)
> + mutex_unlock(&dev->dev_next->lock);
> + else
> + mutex_unlock(&dev->lock);
> + }
> +
> +
> mutex_unlock(&dvb->lock);
> return err;
> }
> diff --git a/drivers/media/usb/em28xx/em28xx.h
> b/drivers/media/usb/em28xx/em28xx.h
> index 953caac..d245c4f 100644
> --- a/drivers/media/usb/em28xx/em28xx.h
> +++ b/drivers/media/usb/em28xx/em28xx.h
> @@ -775,6 +775,7 @@ struct em28xx {
>
> struct em28xx *dev_next;
> int ts;
> + unsigned int *usage_count;
> };
>
> #define kref_to_dev(d) container_of(d, struct em28xx, ref)
