media: v4l: Add a helper for obtaining the link frequency

Add a helper for obtaining the link frequency from transmitter drivers.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/v4l2-core/v4l2-common.c

@@ -441,3 +441,36 @@ int v4l2_fill_pixfmt(struct v4l2_pix_format *pixfmt, u32 pixelformat,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(v4l2_fill_pixfmt);
+
+s64 v4l2_get_link_rate(struct v4l2_ctrl_handler *handler, unsigned int mul,
+		       unsigned int div)
+{
+	struct v4l2_ctrl *ctrl;
+	s64 freq;
+
+	ctrl = v4l2_ctrl_find(handler, V4L2_CID_LINK_FREQ);
+	if (ctrl) {
+		struct v4l2_querymenu qm = { .id = V4L2_CID_LINK_FREQ };
+		int ret;
+
+		qm.index = v4l2_ctrl_g_ctrl(ctrl);
+
+		ret = v4l2_querymenu(handler, &qm);
+		if (ret)
+			return -ENOENT;
+
+		freq = qm.value;
+	} else {
+		if (!mul || !div)
+			return -ENOENT;
+
+		ctrl = v4l2_ctrl_find(handler, V4L2_CID_PIXEL_RATE);
+		if (!ctrl)
+			return -ENOENT;
+
+		freq = div_u64(v4l2_ctrl_g_ctrl_int64(ctrl) * mul, div);
+	}
+
+	return freq > 0 ? freq : -EINVAL;
+}
+EXPORT_SYMBOL_GPL(v4l2_get_link_rate);

include/media/v4l2-common.h

@@ -519,6 +519,27 @@ int v4l2_fill_pixfmt(struct v4l2_pix_format *pixfmt, u32 pixelformat,
 int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat,
 			u32 width, u32 height);
 
+/**
+ * v4l2_get_link_rate - Get link rate from transmitter
+ *
+ * @handler: The transmitter's control handler
+ * @mul: The multiplier between pixel rate and link frequency. Bits per pixel on
+ *	 D-PHY, samples per clock on parallel. 0 otherwise.
+ * @div: The divisor between pixel rate and link frequency. Number of data lanes
+ *	 times two on D-PHY, 1 on parallel. 0 otherwise.
+ *
+ * This function is intended for obtaining the link frequency from the
+ * transmitter sub-devices. It returns the link rate, either from the
+ * V4L2_CID_LINK_FREQ control implemented by the transmitter, or value
+ * calculated based on the V4L2_CID_PIXEL_RATE implemented by the transmitter.
+ *
+ * Returns link frequency on success, otherwise a negative error code:
+ *	-ENOENT: Link frequency or pixel rate control not found
+ *	-EINVAL: Invalid link frequency value
+ */
+s64 v4l2_get_link_rate(struct v4l2_ctrl_handler *handler, unsigned int mul,
+		       unsigned int div);
+
 static inline u64 v4l2_buffer_get_timestamp(const struct v4l2_buffer *buf)
 {
 	/*