Questions about the pixel clock of HDMI

Hi All,
I notice that the pixel clock of HDMI can only be a multiple of 12000000 HZ.

In kernel/drivers/video/tegra/dc/hdmi.c

``````static unsigned long  tegra12x_hdmi_determine_parent(
const struct tegra_dc *dc, struct clk *parent_clk, int pclk)
{
/* T124 hdmi pclk:
*   parentClk = pclk * m  (m=1,1.5,2,2.5,...,128.5)
*   (refclk * n) = pclk * m  (n=1,1.5,2,2.5,...,128.5)
*     (no half resolutions for m due to uneven out duty cycle)
*   (refclk * N / 2) = pclk * m  (N=2,3,4,...,257)
*   m = (refclk / 2 * N) / pclk  (m=1,2,3,...,128)
*     looking for N to make m whole number
*/
int  n, m;
int  b, fr, f;

/* following parameters should come from parent clock */
const int  ref  = 12000000;   /* reference clock to parent */
const int  pmax = 600000000;  /* max freq of parent clock */
b = 0;
fr = 1000;

for (n = 4; (ref / 2 * n) <= pmax; n++) {
if ((ref / 2 * n) < pclk)  /* too low */
continue;
m = DIV_ROUND_UP((ref / 2 * n), (pclk / 1000));
f = m % 1000;  /* fractional parts */
f = (0 == f) ? f : (1000 - f);  /* round-up */
if (0 == f) {  /* exact match */
if ((ref / 2 * b) < 100000000) {
/* parent clock runs at a minumum of 100MHz */
continue;
}
b = n;
fr = f;
break;
} else if (f < fr) {
b = n;
fr = f;
}
}

return (unsigned long)(ref / 2 * b);
}
``````

I would like to know if this is the hardware limitation?
Can we set a specific pixel clock something like 275330000HZ?

FrankPCP,

I just went through the history of this code and it is indeed a hw limitation of TK1. As I understand, even TX1/TX2 cannot give out accurate pclk due to the rounding up and clk limitation.

Hi

If so, what is the case with this release of Xavier? Experience has shown that TX1 / TX2 can set a pixel clock relatively more precisely than TK1, but I wonder if Xavier has improved a bit more. I wonder if it is comparable to the graphics card used for PC or Notebook.

We have a updated driver for xavier and shall be in next release.

When is the next release about?

And if I buy Xavier now, can not I see the HDMI PIXEL CLOCK improvements in the currently released Jetpack compared to TX1 / TX2?