[PATCH 3/3] nvmem: ocotp: Change TIMING calculation algorithm
r.czerwinski at pengutronix.de
Mon Jun 10 23:51:21 PDT 2019
Port of patch from linux-arm-kernel:
| From: Bryan O'Donoghue <pure.logic at nexus-software.ie>
| 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 at pengutronix.de>
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
@@ -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;
+ * 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,
+ strobe_read += 2 * (relax + 1) - 1;
+ strobe_prog = DIV_ROUND_CLOSEST(clk_rate * TIMING_STROBE_PROG_US,
+ strobe_prog += 2 * (relax + 1) - 1;
timing = readl(priv->base + OCOTP_TIMING) & OCOTP_TIMING_WAIT_MASK;
timing |= BF(relax, OCOTP_TIMING_RELAX);
More information about the barebox