linux-kernel - [PATCH v4 06/15] media: mt9m114: Tweak default hblank and vblank for more accurate fps

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Message-Id: <20251224-mt9m114-atomisp-v4-6-60b25da7a1bc@oss.qualcomm.com>
Date: Wed, 24 Dec 2025 13:31:15 +0100
From: Hans de Goede <johannes.goede@....qualcomm.com>
To: Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Hans de Goede <johannes.goede@....qualcomm.com>
Subject: [PATCH v4 06/15] media: mt9m114: Tweak default hblank and vblank
 for more accurate fps

The PLL gets programmed to achieve a 48 MHz pixelclock, with the current
vblank + hblank defaults this results in a fps of:

48000000 / ((1296 + 307) * (976 + 23) = 29.974 fps

Tweak the defaults to get closer to 30 fps:

48000000 / ((1296 + 308) * (976 + 21) = 30.015 fps

This improves things from being 0.026 fps too low to 0.015 fps too high.

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Hans de Goede <johannes.goede@....qualcomm.com>
---
 drivers/media/i2c/mt9m114.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/i2c/mt9m114.c b/drivers/media/i2c/mt9m114.c
index 3fed509055142d7a134cae6cabadde423743178c..d58445826c090f377db473f7926c1b612874ff78 100644
--- a/drivers/media/i2c/mt9m114.c
+++ b/drivers/media/i2c/mt9m114.c
@@ -337,8 +337,8 @@
  */
 #define MT9M114_MIN_HBLANK				303
 #define MT9M114_MIN_VBLANK				21
-#define MT9M114_DEF_HBLANK				307
-#define MT9M114_DEF_VBLANK				23
+#define MT9M114_DEF_HBLANK				308
+#define MT9M114_DEF_VBLANK				21
 
 #define MT9M114_DEF_FRAME_RATE				30
 #define MT9M114_MAX_FRAME_RATE				120

-- 
2.52.0