From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27B4EC43387 for ; Sun, 13 Jan 2019 02:17:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D48F820870 for ; Sun, 13 Jan 2019 02:17:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=sholland.org header.i=@sholland.org header.b="mvmCKr9t"; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="Upeefp0O" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726724AbfAMCR1 (ORCPT ); Sat, 12 Jan 2019 21:17:27 -0500 Received: from out1-smtp.messagingengine.com ([66.111.4.25]:36463 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726629AbfAMCRZ (ORCPT ); Sat, 12 Jan 2019 21:17:25 -0500 Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by mailout.nyi.internal (Postfix) with ESMTP id 663DB23174; Sat, 12 Jan 2019 21:17:23 -0500 (EST) Received: from mailfrontend2 ([10.202.2.163]) by compute5.internal (MEProxy); Sat, 12 Jan 2019 21:17:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sholland.org; h= from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-type:content-transfer-encoding; s=fm1; bh= jKlMXS7XKvXn/szdGKBQgG32+kZpvO4uOo39QB1bolU=; b=mvmCKr9tLbEvZJbP pDROAd6IVm3H+tyjyvewON4VHOYfu+/+ArBujiVhfDXn37l0VEuv9+CnihXwQJz6 4joEh2OkDUy/Q32KvZzaH2GCqpcfAXUzqg4gMHL3z2eF+krzqNFd9EfXRZH4p3zO HP0pa3tHrmZHsG9mnCbzz1JaRXVli6vxQKF/5KOoxpz++tQTllf25u0GpIbfKaOx Z4eKMXxSZvDpYbsxPhgdBnlBZfvOfhsSvTgphvpKdchneqyKUYVjwO68c7ajBeK9 PGEo6YPH30QIE71YUD80IG8ZMrQOWYdlNLKocWTel4ZaJpkw4CIA1H+gnDmSKutJ VDRgYA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:content-type :date:from:in-reply-to:message-id:mime-version:references :subject:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender :x-sasl-enc; s=fm1; bh=jKlMXS7XKvXn/szdGKBQgG32+kZpvO4uOo39QB1bo lU=; b=Upeefp0OZATDpZxWgrtHSzR2/FFiAwyRjS0PC/HWQehfO8m3OS4/AkyP1 L96BnIrJ3Uk4WRUTblFAJvE+dJAiQeJ1WmOsJ+Dkgshp5OGZ0pUhxf/n45Ro4BuL VTC4QqUzoYnFC/ut2gfaL91yRN5tZmU+2ik5O+8E1vvF/IwhZcLDw6tcR/JX6Ixa X+EWoETX3GQC1Dbwzf9yMctarPw5mxJ8ERUyGHtDuFyzr0v0ReMlCfWqdBd0Ekca /EA5D9Um8kl6S9wVk6XgFvZm2vyzRIhfmLQqoEzcCKywrMv2qiCquAYqWMUFIdM+ 3TkvJqkWkNjRz6J6Dbd2i15CpL/Sw== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedtledrfeekgdduvdcutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfhuthenuceurghilhhouhhtmecufedt tdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhephffvufffkffojg hfgggtgfesthekredtredtjeenucfhrhhomhepufgrmhhuvghlucfjohhllhgrnhguuceo shgrmhhuvghlsehshhholhhlrghnugdrohhrgheqnecuffhomhgrihhnpegrrhhmsghirg hnrdgtohhmpdhgihhthhhusgdrtghomhdpfihhihhtvghquhgrrhhkrdhorhhgnecukfhp peejtddrudefhedrudegkedrudehudenucfrrghrrghmpehmrghilhhfrhhomhepshgrmh huvghlsehshhholhhlrghnugdrohhrghenucevlhhushhtvghrufhiiigvpedt X-ME-Proxy: Received: from titanium.stl.sholland.net (70-135-148-151.lightspeed.stlsmo.sbcglobal.net [70.135.148.151]) by mail.messagingengine.com (Postfix) with ESMTPA id 6F2A31026D; Sat, 12 Jan 2019 21:17:21 -0500 (EST) From: Samuel Holland To: Catalin Marinas , Will Deacon , Maxime Ripard , Chen-Yu Tsai , Rob Herring , Mark Rutland , Daniel Lezcano , Thomas Gleixner , Marc Zyngier Cc: devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com, Samuel Holland Subject: [PATCH v3 1/2] arm64: arch_timer: Workaround for Allwinner A64 timer instability Date: Sat, 12 Jan 2019 20:17:18 -0600 Message-Id: <20190113021719.46457-2-samuel@sholland.org> X-Mailer: git-send-email 2.19.2 In-Reply-To: <20190113021719.46457-1-samuel@sholland.org> References: <20190113021719.46457-1-samuel@sholland.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) ======================================================================== 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 Tested-by: Andre Przywara Signed-off-by: Samuel Holland --- Documentation/arm64/silicon-errata.txt | 2 + drivers/clocksource/Kconfig | 10 +++++ drivers/clocksource/arm_arch_timer.c | 55 ++++++++++++++++++++++++++ 3 files changed, 67 insertions(+) diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt index 8f9577621144..4a269732d2a0 100644 --- a/Documentation/arm64/silicon-errata.txt +++ b/Documentation/arm64/silicon-errata.txt @@ -44,6 +44,8 @@ stable kernels. | Implementor | Component | Erratum ID | Kconfig | +----------------+-----------------+-----------------+-----------------------------+ +| Allwinner | A64/R18 | UNKNOWN1 | SUN50I_ERRATUM_UNKNOWN1 | +| | | | | | ARM | Cortex-A53 | #826319 | ARM64_ERRATUM_826319 | | ARM | Cortex-A53 | #827319 | ARM64_ERRATUM_827319 | | ARM | Cortex-A53 | #824069 | ARM64_ERRATUM_824069 | diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig index 55c77e44bb2d..d20ff4da07c3 100644 --- a/drivers/clocksource/Kconfig +++ b/drivers/clocksource/Kconfig @@ -364,6 +364,16 @@ config ARM64_ERRATUM_858921 The workaround will be dynamically enabled when an affected core is detected. +config SUN50I_ERRATUM_UNKNOWN1 + bool "Workaround for Allwinner A64 erratum UNKNOWN1" + default y + depends on ARM_ARCH_TIMER && ARM64 && ARCH_SUNXI + select ARM_ARCH_TIMER_OOL_WORKAROUND + help + This option enables a workaround for instability in the timer on + the Allwinner A64 SoC. The workaround will only be active if the + allwinner,erratum-unknown1 property is found in the timer node. + config ARM_GLOBAL_TIMER bool "Support for the ARM global timer" if COMPILE_TEST select TIMER_OF if OF diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c index 9a7d4dc00b6e..a8b20b65bd4b 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -326,6 +326,48 @@ static u64 notrace arm64_1188873_read_cntvct_el0(void) } #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); @@ -423,6 +465,19 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = { .read_cntvct_el0 = arm64_1188873_read_cntvct_el0, }, #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 }; typedef bool (*ate_match_fn_t)(const struct arch_timer_erratum_workaround *, -- 2.19.2