Hi Hans and others, On Wed, Sep 20, 2017 at 01:24:02PM +0200, Hans Verkuil wrote: > On 09/20/17 13:00, Dave Stevenson wrote: > > On 20 September 2017 at 11:23, Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote: > >> Hi, > >> > >> On Wed, 2017-09-20 at 10:14 +0100, Dave Stevenson wrote: > >>> Hi Mauro & Philipp > >>> > >>> On 19 September 2017 at 17:49, Mauro Carvalho Chehab > >>> <mchehab@xxxxxxxxxxxxxxxx> wrote: > >>>> Em Tue, 19 Sep 2017 17:24:45 +0200 > >>>> Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> escreveu: > >>>> > >>>>> Hi Dave, > >>>>> > >>>>> On Tue, 2017-09-19 at 14:08 +0100, Dave Stevenson wrote: > >>>>>> The existing fixed value of 16 worked for UYVY 720P60 over > >>>>>> 2 lanes at 594MHz, or UYVY 1080P60 over 4 lanes. (RGB888 > >>>>>> 1080P60 needs 6 lanes at 594MHz). > >>>>>> It doesn't allow for lower resolutions to work as the FIFO > >>>>>> underflows. > >>>>>> > >>>>>> Using a value of 300 works for all resolutions down to VGA60, > >>>>>> and the increase in frame delay is <4usecs for 1080P60 UYVY > >>>>>> (2.55usecs for RGB888). > >>>>>> > >>>>>> Signed-off-by: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx> > >>>>> > >>>>> Can we increase this to 320? This would also allow > >>>>> 720p60 at 594 Mbps / 4 lanes, according to the xls. > >>> > >>> Unless I've missed something then the driver would currently request > >>> only 2 lanes for 720p60 UYVY, and that works with the existing FIFO > >>> setting of 16. Likewise 720p60 RGB888 requests 3 lanes and also works > >>> on a FIFO setting of 16. > >>> How/why were you thinking we need to run all four lanes for 720p60 > >>> without other significant driver mods around lane config? > >> > >> The driver currently silently changes the number of active lanes > >> depending on required data rate, with no way to communicate it to the > >> receiver. > > > > It is communicated over the subdevice API - tc358743_g_mbus_config > > reports back the appropriate number of lanes to the receiver > > subdevice. > > A suitable v4l2_subdev_has_op(dev->sensor, video, g_mbus_config) call > > as you're starting streaming therefore gives you the correct > > information. That's what I've just done for the BCM283x Unicam > > driver[1], but admittedly I'm not using the media controller API which > > i.MX6 is. > > Shouldn't this information come from the device tree? The g_mbus_config > op is close to being deprecated or even removed. There are currently only > two obscure V4L2 bridge drivers that call it. It dates from pre-DT times > I rather not see it used in a new bridge driver. > > The problem is that contains data that belongs to the DT (hardware > capabilities). Things that can actually change dynamically should be > communicated via another op. We don't have that, so that should be created. The DT tells how many lanes are connected in hardware, but up to now that's also been the number of lanes actually used. The g_mbus_config() is there, and I'd like to replace that with the more generic frame descriptors, with CSI-2 virtual channel and data type support. They're however not quite ready yet nor I've recently worked on them. I think using g_mbus_config() for the purpose right now is entirely acceptable, we can rework that later on when adding support for frame descriptors. -- Kind regards, Sakari Ailus e-mail: sakari.ailus@xxxxxx
