Re: [PATCH 12/16] gpu: ipu-v3: Fix CSI0 blur in NTSC format

From: Steve Longerbeam
Date: Sat Jul 16 2016 - 16:24:13 EST



On 07/15/2016 04:09 PM, Steve Longerbeam wrote:


On 07/15/2016 05:58 AM, Philipp Zabel wrote:
Am Mittwoch, den 13.07.2016, 16:02 -0700 schrieb Steve Longerbeam:
On 07/10/2016 09:33 AM, Steve Longerbeam wrote:

On 07/08/2016 10:34 AM, Philipp Zabel wrote:
Am Donnerstag, den 07.07.2016, 16:03 -0700 schrieb Steve Longerbeam:
From: Suresh Dhandapani <Suresh.Dhandapani@xxxxxxxxxxxx>

This patch will change the register IPU_CSI0_CCIR_CODE_2 value from
0x40596 to 0x405A6. The change is related to the Start of field 1
first blanking line command bit[5-3] for NTSC format only. This
change is dependent with ADV chip where the NEWAVMODE is set to 0
in register 0x31. Setting NEWAVMODE to "0" in ADV means "EAV/SAV
codes generated to suit analog devices encoders".

Signed-off-by: Suresh Dhandapani <Suresh.Dhandapani@xxxxxxxxxxxx>
---
drivers/gpu/ipu-v3/ipu-csi.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/ipu-v3/ipu-csi.c b/drivers/gpu/ipu-v3/ipu-csi.c
index 0eac28c..ec81958 100644
--- a/drivers/gpu/ipu-v3/ipu-csi.c
+++ b/drivers/gpu/ipu-v3/ipu-csi.c
@@ -422,7 +422,7 @@ int ipu_csi_init_interface(struct ipu_csi *csi,
ipu_csi_write(csi, 0xD07DF | CSI_CCIR_ERR_DET_EN,
CSI_CCIR_CODE_1);
- ipu_csi_write(csi, 0x40596, CSI_CCIR_CODE_2);
+ ipu_csi_write(csi, 0x405A6, CSI_CCIR_CODE_2);
ipu_csi_write(csi, 0xFF0000, CSI_CCIR_CODE_3);
} else {
dev_err(csi->ipu->dev,
This looks like a very hardware specific hack? I'll at least have to
test if that also works with other analog decoders.
Hi Philipp,

Yes it's a hack, but it has always been a hack (hardcoded values). And the
reason is simple, nobody AFAIK (including me) understands how to program
these CSI_CCIR_CODE registers, the description in the reference manual is
complete gibberish.
Hi Philipp, Ian over at linux-media helped me to understand these registers a
little better, although there are still mysteries given the poor documentation.
You should have been copied on that linux-media thread.

The reason we made this change is that, in discussions with Analog Devices,
they recommended setting NEWAVMODE, which changes the positions of
the AV codes sent by the ADV7180 on the bt.656 bus. It took Suresh at least
a full day of reverse engineering (Suresh correct me if I am wrong) to hit
on the correct values in these registers to regain stable video after switching
the ADV7180 to NEWAVMODE.
So this NEWAVMODE is somehow breaking from the BT.656 standard, which
necessitated the change to CSI_CCIR_CODE_2. So NEWAVMODE if enabled in
the ADV7180 will break other capture backends that are expecting standard
BT.656 SAV/EAV codes. So NEWAVMODE should not be used and I will remove
this patch in the next version.
Ok. To use that mode, first a new v4l2 mbus type and corresponding DT
bindings would have to be added.

Hmm, do you mean define something like a V4L2_MBUS_BT656_NEWAVMODE,
and then add a new "newavmode" boolean DT binding parsed by
v4l2_of_parse_endpoint()?

I don't know if that would make sense given that this NEWAVMODE is a kind
of hack of the BT.656 standard, only used by Analog Devices encoders/decoders.

Although there a _lot_ of AD encoder/decoder chips (and subdev drivers written for
them), so maybe it would make sense to do this.


I don't think a "newavmode" boolean property would necessitate a whole new
mbus type, but perhaps just a new parallel bus flag. I will propose a patch at
linux-media that adds this.

Steve