Re: [PATCH v4 23/36] media: imx: Add MIPI CSI-2 Receiver subdev driver

From: Steve Longerbeam
Date: Wed Feb 22 2017 - 19:07:05 EST

On 02/17/2017 03:06 AM, Russell King - ARM Linux wrote:
On Fri, Feb 17, 2017 at 11:47:59AM +0100, Philipp Zabel wrote:
On Wed, 2017-02-15 at 18:19 -0800, Steve Longerbeam wrote:
+static void csi2_dphy_init(struct csi2_dev *csi2)
+ /*
+ * FIXME: 0x14 is derived from a fixed D-PHY reference
+ * clock from the HSI_TX PLL, and a fixed target lane max
+ * bandwidth of 300 Mbps. This value should be derived

If the table in is correct,
this should be 850 Mbps. Where does this 300 Mbps value come from?

I thought you had some code to compute the correct value, although
I guess we've lost the ability to know how fast the sensor is going
to drive the link.

Note that the IMX219 currently drives the data lanes at 912Mbps almost
exclusively, as I've yet to finish working out how to derive the PLL
parameters. (I have something that works, but it currently takes on
the order of 100k iterations to derive the parameters. gcd() doesn't
help you in this instance.)

Hi Russell,

As I mentioned, I've added code to imx6-mipi-csi2 to determine the
sources link frequency via V4L2_CID_LINK_FREQ. If you were to implement
this control and return 912 Mbps-per-lane, the D-PHY will be programmed
correctly for the IMX219 (at least, that is the theory anyway).

Alternatively, I could up the default in imx6-mipi-csi2 to 950
Mbps. I will have to test that to make sure it still works with
OV5640 and tc358743.