[PATCH AUTOSEL 4.19 436/671] nvmem: imx-ocotp: Change TIMING calculation to u-boot algorithm

Sasha Levin
2020-01-16T18:49:46Z

From: Bryan O'Donoghue <pure.logic@nexus-software.ie>

[ Upstream commit 159dbaf57b2f4f67ecb59b2c87d071e45ed41d7e ]

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.

Fixes: 0642bac7da42 ("nvmem: imx-ocotp: add write support")

Signed-off-by: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Suggested-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/nvmem/imx-ocotp.c | 36 ++++++++++++++++++++++++++++++++----
1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/drivers/nvmem/imx-ocotp.c b/drivers/nvmem/imx-ocotp.c
index 04421a73f74a..09281aca86c2 100644
--- a/drivers/nvmem/imx-ocotp.c
+++ b/drivers/nvmem/imx-ocotp.c
@@ -50,7 +50,9 @@
#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
@@ -182,12 +184,38 @@ static void imx_ocotp_set_imx6_timing(struct ocotp_priv *priv)
* 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;
--
2.20.1