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

From: Steve Longerbeam
Date: Wed Jul 13 2016 - 19:02:37 EST

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,
>>> - 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.