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| -rw-r--r-- | target/linux/sunxi/patches-4.19/100-clocksource-drivers-arch_timer-Workaround-for-Allwin.patch | 214 |
1 files changed, 0 insertions, 214 deletions
diff --git a/target/linux/sunxi/patches-4.19/100-clocksource-drivers-arch_timer-Workaround-for-Allwin.patch b/target/linux/sunxi/patches-4.19/100-clocksource-drivers-arch_timer-Workaround-for-Allwin.patch deleted file mode 100644 index 5b9b9dc846..0000000000 --- a/target/linux/sunxi/patches-4.19/100-clocksource-drivers-arch_timer-Workaround-for-Allwin.patch +++ /dev/null @@ -1,214 +0,0 @@ -From 7cd6dca3600d8d71328950216688ecd00015d1ce Mon Sep 17 00:00:00 2001 -From: Samuel Holland <samuel@sholland.org> -Date: Sat, 12 Jan 2019 20:17:18 -0600 -Subject: [PATCH] clocksource/drivers/arch_timer: Workaround for Allwinner A64 - timer instability -MIME-Version: 1.0 -Content-Type: text/plain; charset=UTF-8 -Content-Transfer-Encoding: 8bit - -The Allwinner A64 SoC is known[1] to have an unstable architectural -timer, which manifests itself most obviously in the time jumping forward -a multiple of 95 years[2][3]. This coincides with 2^56 cycles at a -timer frequency of 24 MHz, implying that the time went slightly backward -(and this was interpreted by the kernel as it jumping forward and -wrapping around past the epoch). - -Investigation revealed instability in the low bits of CNTVCT at the -point a high bit rolls over. This leads to power-of-two cycle forward -and backward jumps. (Testing shows that forward jumps are about twice as -likely as backward jumps.) Since the counter value returns to normal -after an indeterminate read, each "jump" really consists of both a -forward and backward jump from the software perspective. - -Unless the kernel is trapping CNTVCT reads, a userspace program is able -to read the register in a loop faster than it changes. A test program -running on all 4 CPU cores that reported jumps larger than 100 ms was -run for 13.6 hours and reported the following: - - Count | Event --------+--------------------------- - 9940 | jumped backward 699ms - 268 | jumped backward 1398ms - 1 | jumped backward 2097ms - 16020 | jumped forward 175ms - 6443 | jumped forward 699ms - 2976 | jumped forward 1398ms - 9 | jumped forward 356516ms - 9 | jumped forward 357215ms - 4 | jumped forward 714430ms - 1 | jumped forward 3578440ms - -This works out to a jump larger than 100 ms about every 5.5 seconds on -each CPU core. - -The largest jump (almost an hour!) was the following sequence of reads: - 0x0000007fffffffff → 0x00000093feffffff → 0x0000008000000000 - -Note that the middle bits don't necessarily all read as all zeroes or -all ones during the anomalous behavior; however the low 10 bits checked -by the function in this patch have never been observed with any other -value. - -Also note that smaller jumps are much more common, with backward jumps -of 2048 (2^11) cycles observed over 400 times per second on each core. -(Of course, this is partially explained by lower bits rolling over more -frequently.) Any one of these could have caused the 95 year time skip. - -Similar anomalies were observed while reading CNTPCT (after patching the -kernel to allow reads from userspace). However, the CNTPCT jumps are -much less frequent, and only small jumps were observed. The same program -as before (except now reading CNTPCT) observed after 72 hours: - - Count | Event --------+--------------------------- - 17 | jumped backward 699ms - 52 | jumped forward 175ms - 2831 | jumped forward 699ms - 5 | jumped forward 1398ms - -Further investigation showed that the instability in CNTPCT/CNTVCT also -affected the respective timer's TVAL register. The following values were -observed immediately after writing CNVT_TVAL to 0x10000000: - - CNTVCT | CNTV_TVAL | CNTV_CVAL | CNTV_TVAL Error ---------------------+------------+--------------------+----------------- - 0x000000d4a2d8bfff | 0x10003fff | 0x000000d4b2d8bfff | +0x00004000 - 0x000000d4a2d94000 | 0x0fffffff | 0x000000d4b2d97fff | -0x00004000 - 0x000000d4a2d97fff | 0x10003fff | 0x000000d4b2d97fff | +0x00004000 - 0x000000d4a2d9c000 | 0x0fffffff | 0x000000d4b2d9ffff | -0x00004000 - -The pattern of errors in CNTV_TVAL seemed to depend on exactly which -value was written to it. For example, after writing 0x10101010: - - CNTVCT | CNTV_TVAL | CNTV_CVAL | CNTV_TVAL Error ---------------------+------------+--------------------+----------------- - 0x000001ac3effffff | 0x1110100f | 0x000001ac4f10100f | +0x1000000 - 0x000001ac40000000 | 0x1010100f | 0x000001ac5110100f | -0x1000000 - 0x000001ac58ffffff | 0x1110100f | 0x000001ac6910100f | +0x1000000 - 0x000001ac66000000 | 0x1010100f | 0x000001ac7710100f | -0x1000000 - 0x000001ac6affffff | 0x1110100f | 0x000001ac7b10100f | +0x1000000 - 0x000001ac6e000000 | 0x1010100f | 0x000001ac7f10100f | -0x1000000 - -I was also twice able to reproduce the issue covered by Allwinner's -workaround[4], that writing to TVAL sometimes fails, and both CVAL and -TVAL are left with entirely bogus values. One was the following values: - - CNTVCT | CNTV_TVAL | CNTV_CVAL ---------------------+------------+-------------------------------------- - 0x000000d4a2d6014c | 0x8fbd5721 | 0x000000d132935fff (615s in the past) -Reviewed-by: Marc Zyngier <marc.zyngier@arm.com> - -======================================================================== - -Because the CPU can read the CNTPCT/CNTVCT registers faster than they -change, performing two reads of the register and comparing the high bits -(like other workarounds) is not a workable solution. And because the -timer can jump both forward and backward, no pair of reads can -distinguish a good value from a bad one. The only way to guarantee a -good value from consecutive reads would be to read _three_ times, and -take the middle value only if the three values are 1) each unique and -2) increasing. This takes at minimum 3 counter cycles (125 ns), or more -if an anomaly is detected. - -However, since there is a distinct pattern to the bad values, we can -optimize the common case (1022/1024 of the time) to a single read by -simply ignoring values that match the error pattern. This still takes no -more than 3 cycles in the worst case, and requires much less code. As an -additional safety check, we still limit the loop iteration to the number -of max-frequency (1.2 GHz) CPU cycles in three 24 MHz counter periods. - -For the TVAL registers, the simple solution is to not use them. Instead, -read or write the CVAL and calculate the TVAL value in software. - -Although the manufacturer is aware of at least part of the erratum[4], -there is no official name for it. For now, use the kernel-internal name -"UNKNOWN1". - -[1]: https://github.com/armbian/build/commit/a08cd6fe7ae9 -[2]: https://forum.armbian.com/topic/3458-a64-datetime-clock-issue/ -[3]: https://irclog.whitequark.org/linux-sunxi/2018-01-26 -[4]: https://github.com/Allwinner-Homlet/H6-BSP4.9-linux/blob/master/drivers/clocksource/arm_arch_timer.c#L272 - -Acked-by: Maxime Ripard <maxime.ripard@bootlin.com> -Tested-by: Andre Przywara <andre.przywara@arm.com> -Signed-off-by: Samuel Holland <samuel@sholland.org> -Cc: stable@vger.kernel.org -Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> ---- - Documentation/arm64/silicon-errata.txt | 2 + - drivers/clocksource/Kconfig | 10 +++++ - drivers/clocksource/arm_arch_timer.c | 55 ++++++++++++++++++++++++++ - 3 files changed, 67 insertions(+) - ---- a/drivers/clocksource/arm_arch_timer.c -+++ b/drivers/clocksource/arm_arch_timer.c -@@ -361,6 +361,48 @@ static u32 notrace sun50i_a64_read_cntv_ - } - #endif - -+#ifdef CONFIG_SUN50I_ERRATUM_UNKNOWN1 -+/* -+ * The low bits of the counter registers are indeterminate while bit 10 or -+ * greater is rolling over. Since the counter value can jump both backward -+ * (7ff -> 000 -> 800) and forward (7ff -> fff -> 800), ignore register values -+ * with all ones or all zeros in the low bits. Bound the loop by the maximum -+ * number of CPU cycles in 3 consecutive 24 MHz counter periods. -+ */ -+#define __sun50i_a64_read_reg(reg) ({ \ -+ u64 _val; \ -+ int _retries = 150; \ -+ \ -+ do { \ -+ _val = read_sysreg(reg); \ -+ _retries--; \ -+ } while (((_val + 1) & GENMASK(9, 0)) <= 1 && _retries); \ -+ \ -+ WARN_ON_ONCE(!_retries); \ -+ _val; \ -+}) -+ -+static u64 notrace sun50i_a64_read_cntpct_el0(void) -+{ -+ return __sun50i_a64_read_reg(cntpct_el0); -+} -+ -+static u64 notrace sun50i_a64_read_cntvct_el0(void) -+{ -+ return __sun50i_a64_read_reg(cntvct_el0); -+} -+ -+static u32 notrace sun50i_a64_read_cntp_tval_el0(void) -+{ -+ return read_sysreg(cntp_cval_el0) - sun50i_a64_read_cntpct_el0(); -+} -+ -+static u32 notrace sun50i_a64_read_cntv_tval_el0(void) -+{ -+ return read_sysreg(cntv_cval_el0) - sun50i_a64_read_cntvct_el0(); -+} -+#endif -+ - #ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND - DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *, timer_unstable_counter_workaround); - EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround); -@@ -451,6 +493,19 @@ static const struct arch_timer_erratum_w - }, - #endif - #ifdef CONFIG_SUN50I_ERRATUM_UNKNOWN1 -+ { -+ .match_type = ate_match_dt, -+ .id = "allwinner,erratum-unknown1", -+ .desc = "Allwinner erratum UNKNOWN1", -+ .read_cntp_tval_el0 = sun50i_a64_read_cntp_tval_el0, -+ .read_cntv_tval_el0 = sun50i_a64_read_cntv_tval_el0, -+ .read_cntpct_el0 = sun50i_a64_read_cntpct_el0, -+ .read_cntvct_el0 = sun50i_a64_read_cntvct_el0, -+ .set_next_event_phys = erratum_set_next_event_tval_phys, -+ .set_next_event_virt = erratum_set_next_event_tval_virt, -+ }, -+#endif -+#ifdef CONFIG_SUN50I_ERRATUM_UNKNOWN1 - { - .match_type = ate_match_dt, - .id = "allwinner,erratum-unknown1", |