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 04421a73f74aa..09281aca86c29 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;