Port of patch from linux-arm-kernel: | From: Bryan O'Donoghue <pure.logic@xxxxxxxxxxxxxxxxx> | | nvmem: imx-ocotp: Change TIMING calculation to u-boot algorithm | | The RELAX field of the OCOTP block is turning out as a zero on i.MX8MM. | This messes up the subsequent re-load of the fuse shadow registers. | | After some discussion with people @ NXP its clear we have missed a trick | here in Linux. | | The OCOTP fuse programming time has a physical minimum 'burn time' that is | not related to the ipg_clk. | | We need to define the RELAX, STROBE_READ and STROBE_PROG fields in terms of | desired timings to allow for the burn-in to safely complete. Right now only | the RELAX field is calculated in terms of an absolute time and we are | ending up with a value of zero. | | This patch inherits the u-boot timings for the OCOTP_TIMING calculation on | the i.MX6 and i.MX8. Those timings are known to work and critically specify | values such as STROBE_PROG as a minimum timing. Signed-off-by: Rouven Czerwinski <r.czerwinski@xxxxxxxxxxxxxx> --- drivers/nvmem/ocotp.c | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) diff --git a/drivers/nvmem/ocotp.c b/drivers/nvmem/ocotp.c index c21327805b..3f9f162860 100644 --- a/drivers/nvmem/ocotp.c +++ b/drivers/nvmem/ocotp.c @@ -69,7 +69,9 @@ /* Other definitions */ #define IMX6_OTP_DATA_ERROR_VAL 0xBADABADA -#define DEF_RELAX 20 +#define TIMING_STROBE_PROG_US 10 +#define TIMING_STROBE_READ_NS 37 +#define TIMING_RELAX_NS 17 #define MAC_OFFSET_0 (0x22 * 4) #define IMX6UL_MAC_OFFSET_1 (0x23 * 4) #define MAC_OFFSET_1 (0x24 * 4) @@ -119,11 +121,39 @@ static int imx6_ocotp_set_timing(struct ocotp_priv *priv) u32 relax, strobe_read, strobe_prog; u32 timing; + /* + * 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 + OCOTP_TIMING) & OCOTP_TIMING_WAIT_MASK; timing |= BF(relax, OCOTP_TIMING_RELAX); -- 2.22.0 _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
