linux-kernel - [PATCH] media: i2c: adv748x: initialize bit 7 of csi_tx_top_reg

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Date:   Fri, 10 May 2019 17:30:40 +0200
From:   Michael Rodin <mrodin@...adit-jv.com>
To:     <kieran.bingham@...asonboard.com>, <mchehab@...nel.org>,
        <linux-media@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <michael@...in.online>,
        <mrodin@...adit-jv.com>
Subject: [PATCH] media: i2c: adv748x: initialize bit 7 of csi_tx_top_reg_1f

According to pages 188 and 193 of the "UG-747: ADV7481 Reference Manual"
[1], the bit 7 (FRAMENUMBER_INTERLACED) of the register csi_tx_top_reg_1f
"sets association of frame number in the FS and FE packets with the F bit
in the EAV/SAV codes". EAV/SAV codes are defined in [2].
According to [2]:
F=0 for field 1
F=1 for field 2
The bit FRAMENUMBER_INTERLACED is not initialized anywhere in the current
version of the adv748x driver and therefore it is always 0, which is the
default value according to [1]. Therefore the current association of field
number from EAV/SAV code with the frame number in CSI FS and FE packets is:
field 1 (top field for PAL, bottom field for NTSC) -> CSI frame number 2
field 2 (bottom field for PAL, top field for NTSC) -> CSI frame number 1
But this breaks frame number based field detection of top/bottom fields
in CSI receivers. Therefore it makes sense to initialize the
FRAMENUMBER_INTERLACED bit to 1 so the association is as expected:
field 1 -> frame number 1
field 2 -> frame number 2

[1] https://www.analog.com/en/products/adv7481.html
[2] https://www.itu.int/rec/R-REC-BT.656-5-200712-I/en

Suggested-by: Steve Longerbeam <steve_longerbeam@...tor.com>
Signed-off-by: Michael Rodin <mrodin@...adit-jv.com>
---
 drivers/media/i2c/adv748x/adv748x-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/media/i2c/adv748x/adv748x-core.c b/drivers/media/i2c/adv748x/adv748x-core.c
index f57cd77..4dd1a13 100644
--- a/drivers/media/i2c/adv748x/adv748x-core.c
+++ b/drivers/media/i2c/adv748x/adv748x-core.c
@@ -278,6 +278,9 @@ static int adv748x_power_up_tx(struct adv748x_csi2 *tx)
 	usleep_range(1000, 1500);
 	adv748x_write_check(state, page, 0x31, 0x80, &ret);

+	/* set bit 7 (FRAMENUMBER_INTERLACED) in csi_tx_top_reg_1f */
+	adv748x_write_check(state, page, 0x1f, 0x80, &ret);
+
 	return ret;
 }

-- 
2.7.4