[PATCH v4 3/3] media: mgb4: Fixed signal frame rate limit handling

[tumic@gpxsee.org]

From: Martin Tůma <martin.tuma@digiteqautomotive.com>

Properly document the function of the mgb4 output frame_rate sysfs parameter
and fix the corner case when the frame rate is set to zero causing a "divide
by zero" kernel panic.

Signed-off-by: Martin Tůma <martin.tuma@digiteqautomotive.com>
---
 Documentation/admin-guide/media/mgb4.rst |  8 ++++++--
 drivers/media/pci/mgb4/mgb4_sysfs_out.c  |  9 +++++----
 drivers/media/pci/mgb4/mgb4_vout.c       | 12 ++++++------
 drivers/media/pci/mgb4/mgb4_vout.h       |  2 +-
 4 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/Documentation/admin-guide/media/mgb4.rst b/Documentation/admin-guide/media/mgb4.rst
index 2977f74d7e26..6fff886003e2 100644
--- a/Documentation/admin-guide/media/mgb4.rst
+++ b/Documentation/admin-guide/media/mgb4.rst
@@ -228,8 +228,12 @@ Common FPDL3/GMSL output parameters
     open.*
 
 **frame_rate** (RW):
-    Output video frame rate in frames per second. The default frame rate is
-    60Hz.
+    Output video signal frame rate limit in frames per second. Due to
+    the limited output pixel clock steps, the card can not always generate
+    a frame rate perfectly matching the value required by the connected display.
+    Using this parameter one can limit the frame rate by "crippling" the signal
+    so that the lines are not equal but the signal appears like having the exact
+    frame rate to the connected display. The default frame rate limit is 60Hz.
 
 **hsync_polarity** (RW):
     HSYNC signal polarity.
diff --git a/drivers/media/pci/mgb4/mgb4_sysfs_out.c b/drivers/media/pci/mgb4/mgb4_sysfs_out.c
index f67ff2a48329..573aa61c69d4 100644
--- a/drivers/media/pci/mgb4/mgb4_sysfs_out.c
+++ b/drivers/media/pci/mgb4/mgb4_sysfs_out.c
@@ -229,9 +229,9 @@ static ssize_t frame_rate_show(struct device *dev,
 	struct video_device *vdev = to_video_device(dev);
 	struct mgb4_vout_dev *voutdev = video_get_drvdata(vdev);
 	u32 period = mgb4_read_reg(&voutdev->mgbdev->video,
-				   voutdev->config->regs.frame_period);
+				   voutdev->config->regs.frame_limit);
 
-	return sprintf(buf, "%u\n", MGB4_HW_FREQ / period);
+	return sprintf(buf, "%u\n", period ? MGB4_HW_FREQ / period : 0);
 }
 
 /*
@@ -245,14 +245,15 @@ static ssize_t frame_rate_store(struct device *dev,
 	struct video_device *vdev = to_video_device(dev);
 	struct mgb4_vout_dev *voutdev = video_get_drvdata(vdev);
 	unsigned long val;
-	int ret;
+	int limit, ret;
 
 	ret = kstrtoul(buf, 10, &val);
 	if (ret)
 		return ret;
 
+	limit = val ? MGB4_HW_FREQ / val : 0;
 	mgb4_write_reg(&voutdev->mgbdev->video,
-		       voutdev->config->regs.frame_period, MGB4_HW_FREQ / val);
+		       voutdev->config->regs.frame_limit, limit);
 
 	return count;
 }
diff --git a/drivers/media/pci/mgb4/mgb4_vout.c b/drivers/media/pci/mgb4/mgb4_vout.c
index a6b55669f0a8..cd001ceaae63 100644
--- a/drivers/media/pci/mgb4/mgb4_vout.c
+++ b/drivers/media/pci/mgb4/mgb4_vout.c
@@ -680,12 +680,12 @@ static void fpga_init(struct mgb4_vout_dev *voutdev)
 	mgb4_write_reg(video, regs->config, 0x00000011);
 	mgb4_write_reg(video, regs->resolution,
 		       (DEFAULT_WIDTH << 16) | DEFAULT_HEIGHT);
-	mgb4_write_reg(video, regs->hsync, 0x00102020);
-	mgb4_write_reg(video, regs->vsync, 0x40020202);
-	mgb4_write_reg(video, regs->frame_period, DEFAULT_PERIOD);
+	mgb4_write_reg(video, regs->hsync, 0x00283232);
+	mgb4_write_reg(video, regs->vsync, 0x40141F1E);
+	mgb4_write_reg(video, regs->frame_limit, DEFAULT_PERIOD);
 	mgb4_write_reg(video, regs->padding, 0x00000000);
 
-	voutdev->freq = mgb4_cmt_set_vout_freq(voutdev, 70000 >> 1) << 1;
+	voutdev->freq = mgb4_cmt_set_vout_freq(voutdev, 61150 >> 1) << 1;
 
 	mgb4_write_reg(video, regs->config,
 		       (voutdev->config->id + MGB4_VIN_DEVICES) << 2 | 1 << 4);
@@ -711,8 +711,8 @@ static void debugfs_init(struct mgb4_vout_dev *voutdev)
 	voutdev->regs[3].offset = voutdev->config->regs.hsync;
 	voutdev->regs[4].name = "VIDEO_PARAMS_2";
 	voutdev->regs[4].offset = voutdev->config->regs.vsync;
-	voutdev->regs[5].name = "FRAME_PERIOD";
-	voutdev->regs[5].offset = voutdev->config->regs.frame_period;
+	voutdev->regs[5].name = "FRAME_LIMIT";
+	voutdev->regs[5].offset = voutdev->config->regs.frame_limit;
 	voutdev->regs[6].name = "PADDING_PIXELS";
 	voutdev->regs[6].offset = voutdev->config->regs.padding;
 	if (has_timeperframe(video)) {
diff --git a/drivers/media/pci/mgb4/mgb4_vout.h b/drivers/media/pci/mgb4/mgb4_vout.h
index ab9b58b1deb7..adc8fe1e7ae6 100644
--- a/drivers/media/pci/mgb4/mgb4_vout.h
+++ b/drivers/media/pci/mgb4/mgb4_vout.h
@@ -19,7 +19,7 @@ struct mgb4_vout_regs {
 	u32 config;
 	u32 status;
 	u32 resolution;
-	u32 frame_period;
+	u32 frame_limit;
 	u32 hsync;
 	u32 vsync;
 	u32 padding;
-- 
2.44.0