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

[Steve Longerbeam]

On 02/22/2017 04:06 PM, Steve Longerbeam wrote:
> 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 https://community.nxp.com/docs/DOC-94312 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,

argh, I mean return 912 / 2.

Steve

 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.
>
> Steve