nvmem: imx-ocotp: Change TIMING calculation to u-boot algorithm

#define IMX_OCOTP_BM_CTRL_ERROR		0x00000200

#define IMX_OCOTP_BM_CTRL_REL_SHADOWS	0x00000400

#define DEF_RELAX			20	/* > 16.5ns */

#define TIMING_STROBE_PROG_US		10	/* Min time to blow a fuse */

#define TIMING_STROBE_READ_NS		37	/* Min time before read */

#define TIMING_RELAX_NS			17

#define DEF_FSOURCE			1001	/* > 1000 ns */

#define DEF_STROBE_PROG			10000	/* IPG clocks */

#define IMX_OCOTP_WR_UNLOCK		0x3E770000

	 * fields with timing values to match the current frequency of the

	 * ipg_clk. OTP writes will work at maximum bus frequencies as long

	 * as the HW_OCOTP_TIMING parameters are set correctly.

	 *

	 * Note: there are minimum timings required to ensure an OTP fuse burns

	 * correctly that are independent of the ipg_clk. Those values are not

	 * formally documented anywhere however, working from the minimum

	 * timings given in u-boot we can say:

	 *

	 * - Minimum STROBE_PROG time is 10 microseconds. Intuitively 10

	 *   microseconds feels about right as representative of a minimum time

	 *   to physically burn out a fuse.

	 *

	 * - Minimum STROBE_READ i.e. the time to wait post OTP fuse burn before

	 *   performing another read is 37 nanoseconds

	 *

	 * - Minimum RELAX timing is 17 nanoseconds. This final RELAX minimum

	 *   timing is not entirely clear the documentation says "This

	 *   count value specifies the time to add to all default timing

	 *   parameters other than the Tpgm and Trd. It is given in number

	 *   of ipg_clk periods." where Tpgm and Trd refer to STROBE_PROG

	 *   and STROBE_READ respectively. What the other timing parameters

	 *   are though, is not specified. Experience shows a zero RELAX

	 *   value will mess up a re-load of the shadow registers post OTP

	 *   burn.

	 */

	clk_rate = clk_get_rate(priv->clk);

	relax = clk_rate / (1000000000 / DEF_RELAX) - 1;

	strobe_prog = clk_rate / (1000000000 / 10000) + 2 * (DEF_RELAX + 1) - 1;

	strobe_read = clk_rate / (1000000000 / 40) + 2 * (DEF_RELAX + 1) - 1;

	relax = DIV_ROUND_UP(clk_rate * TIMING_RELAX_NS, 1000000000) - 1;

	strobe_read = DIV_ROUND_UP(clk_rate * TIMING_STROBE_READ_NS,

				   1000000000);

	strobe_read += 2 * (relax + 1) - 1;

	strobe_prog = DIV_ROUND_CLOSEST(clk_rate * TIMING_STROBE_PROG_US,

					1000000);

	strobe_prog += 2 * (relax + 1) - 1;

	timing = readl(priv->base + IMX_OCOTP_ADDR_TIMING) & 0x0FC00000;

	timing |= strobe_prog & 0x00000FFF;