From patchwork Thu Mar 8 04:21:10 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yasushi SHOJI X-Patchwork-Id: 882961 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=lists.denx.de (client-ip=81.169.180.215; helo=lists.denx.de; envelope-from=u-boot-bounces@lists.denx.de; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=gmail.com Received: from lists.denx.de (dione.denx.de [81.169.180.215]) by ozlabs.org (Postfix) with ESMTP id 3zxcmX0103z9scb for ; Thu, 8 Mar 2018 15:22:19 +1100 (AEDT) Received: by lists.denx.de (Postfix, from userid 105) id AF708C21F5B; Thu, 8 Mar 2018 04:22:13 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on lists.denx.de X-Spam-Level: X-Spam-Status: No, score=0.0 required=5.0 tests=FREEMAIL_FROM autolearn=unavailable autolearn_force=no version=3.4.0 Received: from lists.denx.de (localhost [IPv6:::1]) by lists.denx.de (Postfix) with ESMTP id 2B0D1C21E52; Thu, 8 Mar 2018 04:22:11 +0000 (UTC) Received: by lists.denx.de (Postfix, from userid 105) id 64EE4C21E52; Thu, 8 Mar 2018 04:22:09 +0000 (UTC) Received: from sv-prius.atmark-techno.com (sodcd-04p2-40.ppp11.odn.ad.jp [203.139.65.40]) by lists.denx.de (Postfix) with ESMTP id 9DC92C21C2F for ; Thu, 8 Mar 2018 04:22:08 +0000 (UTC) Received: from leno.local-network (unknown [172.16.1.247]) by sv-prius.atmark-techno.com (Postfix) with ESMTP id 2A7C43F828; Thu, 8 Mar 2018 13:22:04 +0900 (JST) From: Yasushi SHOJI To: trini@konsulko.com Date: Thu, 8 Mar 2018 13:21:10 +0900 Message-Id: <20180308042110.30538-1-yasushi.shoji@gmail.com> X-Mailer: git-send-email 2.16.2 Cc: fabio.estevam@nxp.com, u-boot@lists.denx.de Subject: [U-Boot] [PATCH] imx: syscounter: make sure asm is volatile X-BeenThere: u-boot@lists.denx.de X-Mailman-Version: 2.1.18 Precedence: list List-Id: U-Boot discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: u-boot-bounces@lists.denx.de Sender: "U-Boot" Without the volatile attribute, compilers are entitled to optimize out the same asm(). In the case of __udelay() in syscounter.c, it calls `get_ticks()` twice, one for the starting time and the second in the loop to check the current time. When compilers inline `get_ticks()` they see the same `mrrc` instructions and optimize out the second one. This leads to infinite loop since we don't get updated value from the system counter. Here is a portion of the disassembly of __udelay: 88: 428b cmp r3, r1 8a: f8ce 20a4 str.w r2, [lr, #164] ; 0xa4 8e: bf08 it eq 90: 4282 cmpeq r2, r0 92: f8ce 30a0 str.w r3, [lr, #160] ; 0xa0 96: d3f7 bcc.n 88 <__udelay+0x88> 98: e8bd 8cf0 ldmia.w sp!, {r4, r5, r6, r7, sl, fp, pc} Note that final jump / loop at 96 to 88, we don't have any `mrrc`. With a volatile attribute, the above changes to this: 8a: ec53 2f0e mrrc 15, 0, r2, r3, cr14 8e: 42ab cmp r3, r5 90: f8c1 20a4 str.w r2, [r1, #164] ; 0xa4 94: bf08 it eq 96: 42a2 cmpeq r2, r4 98: f8c1 30a0 str.w r3, [r1, #160] ; 0xa0 9c: d3f5 bcc.n 8a <__udelay+0x8a> 9e: e8bd 8cf0 ldmia.w sp!, {r4, r5, r6, r7, sl, fp, pc} a2: bf00 nop I'm advised[1] to put volatile on all asm(), so this commit also adds it to the asm() in timer_init(). [1]: https://lists.denx.de/pipermail/u-boot/2018-March/322062.html Signed-off-by: Yasushi SHOJI Reviewed-by: Fabio Estevam --- arch/arm/mach-imx/syscounter.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm/mach-imx/syscounter.c b/arch/arm/mach-imx/syscounter.c index 9290918dca..1d4ebfe343 100644 --- a/arch/arm/mach-imx/syscounter.c +++ b/arch/arm/mach-imx/syscounter.c @@ -62,7 +62,7 @@ int timer_init(void) unsigned long val, freq; freq = CONFIG_SC_TIMER_CLK; - asm("mcr p15, 0, %0, c14, c0, 0" : : "r" (freq)); + asm volatile("mcr p15, 0, %0, c14, c0, 0" : : "r" (freq)); writel(freq, &sctr->cntfid0); @@ -82,7 +82,7 @@ unsigned long long get_ticks(void) { unsigned long long now; - asm("mrrc p15, 0, %Q0, %R0, c14" : "=r" (now)); + asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (now)); gd->arch.tbl = (unsigned long)(now & 0xffffffff); gd->arch.tbu = (unsigned long)(now >> 32);