From nobody Sun Feb 8 21:32:55 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9E21C001DF for ; Tue, 1 Aug 2023 16:28:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229650AbjHAQ2K (ORCPT ); Tue, 1 Aug 2023 12:28:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54304 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229457AbjHAQ2I (ORCPT ); Tue, 1 Aug 2023 12:28:08 -0400 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 79CD9133 for ; Tue, 1 Aug 2023 09:28:07 -0700 (PDT) Received: from drehscheibe.grey.stw.pengutronix.de ([2a0a:edc0:0:c01:1d::a2]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1qQsDv-00018q-Q3; Tue, 01 Aug 2023 18:27:51 +0200 Received: from [2a0a:edc0:0:1101:1d::54] (helo=dude05.red.stw.pengutronix.de) by drehscheibe.grey.stw.pengutronix.de with esmtp (Exim 4.94.2) (envelope-from ) id 1qQsDu-000QYa-SP; Tue, 01 Aug 2023 18:27:50 +0200 Received: from afa by dude05.red.stw.pengutronix.de with local (Exim 4.96) (envelope-from ) id 1qQsDt-00Dkrt-2z; Tue, 01 Aug 2023 18:27:49 +0200 From: Ahmad Fatoum To: Abel Vesa , Peng Fan , Michael Turquette , Stephen Boyd , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team Cc: Ahmad Fatoum , linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH] clk: imx: composite-8m: avoid glitches when set_rate would be a no-op Date: Tue, 1 Aug 2023 18:27:31 +0200 Message-Id: <20230801162731.3278396-1-a.fatoum@pengutronix.de> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-SA-Exim-Connect-IP: 2a0a:edc0:0:c01:1d::a2 X-SA-Exim-Mail-From: afa@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Reconfiguring the clock divider to the exact same value is observed on an i.MX8MN to often cause a short clock pause, probably because the divider restarts counting from the time the register is written. This issue doesn't show up normally, because the clock framework will take care to not call set_rate when the clock rate is the same. However, when we configure an upstream clock (e.g. an audio_pll), the common code will call set_rate with the newly calculated rate on all children. As the new rate is different, we enter set_rate and compute the same divider values, write them back and cause the glitch (e.g. on a SAI's MCLK). To avoid the glitch, we skip writing the same value back again. Fixes: d3ff9728134e ("clk: imx: Add imx composite clock") Signed-off-by: Ahmad Fatoum Reviewed-by: Marco Felsch --- drivers/clk/imx/clk-composite-8m.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/clk/imx/clk-composite-8m.c b/drivers/clk/imx/clk-compo= site-8m.c index cbf0d7955a00..3e9a092e136c 100644 --- a/drivers/clk/imx/clk-composite-8m.c +++ b/drivers/clk/imx/clk-composite-8m.c @@ -97,7 +97,7 @@ static int imx8m_clk_composite_divider_set_rate(struct cl= k_hw *hw, int prediv_value; int div_value; int ret; - u32 val; + u32 orig, val; =20 ret =3D imx8m_clk_composite_compute_dividers(rate, parent_rate, &prediv_value, &div_value); @@ -106,13 +106,15 @@ static int imx8m_clk_composite_divider_set_rate(struc= t clk_hw *hw, =20 spin_lock_irqsave(divider->lock, flags); =20 - val =3D readl(divider->reg); - val &=3D ~((clk_div_mask(divider->width) << divider->shift) | - (clk_div_mask(PCG_DIV_WIDTH) << PCG_DIV_SHIFT)); + orig =3D readl(divider->reg); + val =3D orig & ~((clk_div_mask(divider->width) << divider->shift) | + (clk_div_mask(PCG_DIV_WIDTH) << PCG_DIV_SHIFT)); =20 val |=3D (u32)(prediv_value - 1) << divider->shift; val |=3D (u32)(div_value - 1) << PCG_DIV_SHIFT; - writel(val, divider->reg); + + if (val !=3D orig) + writel(val, divider->reg); =20 spin_unlock_irqrestore(divider->lock, flags); =20 --=20 2.39.2