Re: [PATCH v6 2/3] media: imx: add a driver for i.MX8MQ mipi csi rx phy and controller
From: Laurent Pinchart
Date: Thu Jul 15 2021 - 17:52:30 EST
Hi Martin,
On Thu, Jul 15, 2021 at 09:37:24AM +0200, Martin Kepplinger wrote:
> Am Mittwoch, dem 14.07.2021 um 21:24 +0300 schrieb Laurent Pinchart:
> > On Wed, Jul 14, 2021 at 01:19:30PM +0200, Martin Kepplinger wrote:
> > > Add a driver to support the i.MX8MQ MIPI CSI receiver. The hardware side
> > > is based on
> > > https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/media/platform/imx8/mxc-mipi-csi2_yav.c?h=imx_5.4.70_2.3.0
> > >
> > > It's built as part of VIDEO_IMX7_CSI because that's documented to support
> > > i.MX8M platforms. This driver adds i.MX8MQ support where currently only the
> > > i.MX8MM platform has been supported.
> > >
> > > Signed-off-by: Martin Kepplinger <martin.kepplinger@xxxxxxx>
> > > ---
> > > drivers/staging/media/imx/Makefile | 1 +
> > > drivers/staging/media/imx/imx8mq-mipi-csi2.c | 949 +++++++++++++++++++
> > > 2 files changed, 950 insertions(+)
> > > create mode 100644 drivers/staging/media/imx/imx8mq-mipi-csi2.c
> > >
> > > diff --git a/drivers/staging/media/imx/Makefile
> > > b/drivers/staging/media/imx/Makefile
> > > index 6ac33275cc97..19c2fc54d424 100644
> > > --- a/drivers/staging/media/imx/Makefile
> > > +++ b/drivers/staging/media/imx/Makefile
> > > @@ -16,3 +16,4 @@ obj-$(CONFIG_VIDEO_IMX_CSI) += imx6-mipi-csi2.o
[snip]
> > > +static int imx8mq_mipi_csi_calc_hs_settle(struct csi_state *state)
> > > +{
> > > + u32 width = state->format_mbus[MIPI_CSI2_PAD_SINK].width;
> > > + u32 height = state->format_mbus[MIPI_CSI2_PAD_SINK].height;
> > > + s64 link_freq;
> > > + u32 lane_rate;
> > > +
> > > + /* Calculate the line rate from the pixel rate. */
> > > + link_freq = v4l2_get_link_freq(state->src_sd->ctrl_handler,
> > > + state->csi2_fmt->width,
> > > + state->bus.num_data_lanes * 2);
> > > + if (link_freq < 0) {
> > > + dev_err(state->dev, "Unable to obtain link frequency: %d\n",
> > > + (int)link_freq);
> > > + return link_freq;
> > > + }
> > > +
> > > + lane_rate = link_freq * 2;
> > > + if (lane_rate < 80000000 || lane_rate > 1500000000) {
> > > + dev_dbg(state->dev, "Out-of-bound lane rate %u\n", lane_rate);
> > > + return -EINVAL;
> > > + }
> > > +
> > > + /* https://community.nxp.com/t5/i-MX-Processors/Explenation-for-HS-SETTLE-parameter-in-MIPI-CSI-D-PHY-registers/m-p/764275/highlight/true#M118744 */
> > > + if (lane_rate < 250000000)
> > > + state->hs_settle = 0xb;
> > > + else if (lane_rate < 500000000)
> > > + state->hs_settle = 0x8;
> > > + else
> > > + state->hs_settle = 0x6;
> >
> > We could possibly compute this value based on the formula from the table
> > in that page, but maybe that's overkill ? If you want to give it a try,
> > it would be along those lines.
> >
> > /*
> > * The D-PHY specification requires Ths-settle to be in the range
> > * 85ns + 6*UI to 140ns + 10*UI, with the unit interval UI being half
> > * the clock period.
> > *
> > * The Ths-settle value is expressed in the hardware as a multiple of
> > * the Esc clock period:
> > *
> > * Ths-settle = (PRG_RXHS_SETTLE + 1) * Tperiod of RxClkInEsc
> > *
> > * Due to the one cycle inaccuracy introduced by rounding, the
> > * documentation recommends picking a value away from the boundaries.
> > * Let's pick the average.
> > */
> > esc_clk_rate = clk_get_rate(...);
> >
> > min_ths_settle = 85 + 6 * 1000000 / (lane_rate / 1000);
> > max_ths_settle = 140 + 10 * 1000000 / (lane_rate / 1000);
> > ths_settle = (min_ths_settle + max_ths_settle) / 2;
> >
> > state->hs_settle = ths_settle * esc_clk_rate / 1000000000 - 1;
>
> I experimented a bit but would like to leave this as a task for later
> if that's ok. it's correct and simple now. also, using clks[i].clk
> based on the name string would feel better to submit seperately later.
That's OK with me, but I may then submit a patch on top fairly soon :-)
Have you been able to test if this code works on your device ? The main
reason why I think it's better is that it doesn't hardcode a specific
escape clock frequency assumption, so it should be able to accommodate a
wider range of use cases. If we change it later, there's always a risk
of regressions, while if we do this from the start, we'll figure out
quickly if it doesn't work in some cases.
--
Regards,
Laurent Pinchart