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.
The i.MX6 MIPI CSI-2 receiver driver can't cope with that, as it always
activates all four lanes that are configured in the device tree. I can
work around that with the following patch:
----------8<----------
Subject: [PATCH] [media] tc358743: do not dynamically reduce number of lanes
Dynamic lane number reduction does not work with receivers that
configure a fixed lane number according to the device tree settings.
To allow 720p60 at 594 Mbit/s on 4 lanes, increase the fifo_level
and tclk_trailcnt settings.
Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
---
drivers/media/i2c/tc358743.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/media/i2c/tc358743.c b/drivers/media/i2c/tc358743.c
index 64f504542a819..70a9435928cdb 100644
--- a/drivers/media/i2c/tc358743.c
+++ b/drivers/media/i2c/tc358743.c
@@ -683,7 +683,7 @@ static void tc358743_set_csi(struct v4l2_subdev *sd)
{
struct tc358743_state *state = to_state(sd);
struct tc358743_platform_data *pdata = &state->pdata;
- unsigned lanes = tc358743_num_csi_lanes_needed(sd);
+ unsigned lanes = state->bus.num_data_lanes;
v4l2_dbg(3, debug, sd, "%s:\n", __func__);
@@ -1906,7 +1906,7 @@ static int tc358743_probe_of(struct tc358743_state *state)
state->pdata.ddc5v_delay = DDC5V_DELAY_100_MS;
state->pdata.enable_hdcp = false;
/* A FIFO level of 16 should be enough for 2-lane 720p60 at 594 MHz. */
- state->pdata.fifo_level = 16;
+ state->pdata.fifo_level = 320;
/*
* The PLL input clock is obtained by dividing refclk by pll_prd.
* It must be between 6 MHz and 40 MHz, lower frequency is better.
@@ -1948,7 +1948,7 @@ static int tc358743_probe_of(struct tc358743_state *state)
state->pdata.lptxtimecnt = 0x003;
/* tclk-preparecnt: 3, tclk-zerocnt: 20 */
state->pdata.tclk_headercnt = 0x1403;
- state->pdata.tclk_trailcnt = 0x00;
+ state->pdata.tclk_trailcnt = 0x01;
/* ths-preparecnt: 3, ths-zerocnt: 1 */
state->pdata.ths_headercnt = 0x0103;
state->pdata.twakeup = 0x4882;
--
2.11.0
---------->8----------
Just adding the same heuristic as tc358743_num_csi_lanes_needed in the
imx6-mipi-csi2 driver doesn't work, as the heuristic is specific to the
Toshiba chip. There are MIPI CSI-2 sensors that only support a fixed
number of lanes, for example.
I'd need a way to communicate the number of active MIPI CSI-2 lanes
between transmitting and receiving subdevice driver.
> Once I've got a v3 done on the Unicam driver I'll bash through the
> standard HDMI modes and check what value they need - I can see a big
> spreadsheet coming on.
Oh dear. Unless the point you make below can be resolved, I think we
have no other choice.
> I'll ignore interlaced modes as I can't see any support for it in the
> driver. Receiving the fields on different CSI-2 data types is
> something I know the Unicam hardware won't handle nicely, and I
> suspect it'd be an issue for many other platforms too.
Yes, let's pretend interlacing doesn't exist as long as possible.
> > Hmm... if this is dependent on the resolution and frame rate,
> > wouldn't
> > it be better to dynamically adjust it accordingly?
>
> It's setting up the FIFO matching the incoming HDMI data rate and
> outgoing CSI rate. That means it's dependent on the incoming pixel
> clock, blanking, colour format and resolution, and output CSI link
> frequency, number of lanes, and colour format.
> Whilst it could be set dynamically based on all those parameters, is
> there a significant enough gain in doing so?
Ideally there would be no need to maintain a timing database with -
worst case - (number of link frequencies * number of HDMI modes) entries
in the driver ...
> The value of 300 works for all cases I've tried, and referencing back
> it is also the value that Hans said Cisco use via platform data on
> their hardware [1]. Generally I'm seeing that values of 0-130 are
> required, so 300 is giving a fair safety margin.
It does not work for 720p60 on 4 lanes at 594 Mbit/s, as the spreadsheet
warns, and testing shows.
> Second question is does anyone have a suitable relationship with
> Toshiba to get permission to release details of these register
> calculations? The datasheet and value spreadsheet are marked as
> confidential, and probably under NDA in almost all cases. Whilst they
> can't object to drivers containing values to make them work, they
> might over releasing significant details.
Unfortunately, I don't.
regards
Philipp
