From patchwork Thu Aug 12 17:00:22 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Shevchenko X-Patchwork-Id: 496083 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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 3420AC4320A for ; Thu, 12 Aug 2021 17:00:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 150BB6109F for ; Thu, 12 Aug 2021 17:00:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233957AbhHLRBH (ORCPT ); Thu, 12 Aug 2021 13:01:07 -0400 Received: from mga12.intel.com ([192.55.52.136]:62812 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233875AbhHLRBG (ORCPT ); Thu, 12 Aug 2021 13:01:06 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10074"; a="194987169" X-IronPort-AV: E=Sophos;i="5.84,316,1620716400"; d="scan'208";a="194987169" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Aug 2021 10:00:34 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.84,316,1620716400"; d="scan'208";a="571539798" Received: from black.fi.intel.com ([10.237.72.28]) by orsmga004.jf.intel.com with ESMTP; 12 Aug 2021 10:00:29 -0700 Received: by black.fi.intel.com (Postfix, from userid 1003) id 13C93B1; Thu, 12 Aug 2021 20:00:28 +0300 (EEST) From: Andy Shevchenko To: "Rafael J. Wysocki" , Andy Shevchenko , Heiko Stuebner , Elaine Zhang , Stephen Boyd , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-clk@vger.kernel.org, linux-imx@nxp.com, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org Cc: "Rafael J. Wysocki" , Len Brown , Michael Turquette , Abel Vesa , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Lee Jones Subject: [PATCH v4 1/4] clk: fractional-divider: Export approximation algorithm to the CCF users Date: Thu, 12 Aug 2021 20:00:22 +0300 Message-Id: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org At least one user currently duplicates some functions that are provided by fractional divider module. Let's export approximation algorithm and replace the open-coded variant. As a bonus the exported function will get better documentation in place. Signed-off-by: Andy Shevchenko Tested-by: Heiko Stuebner Acked-by: Heiko Stuebner --- v4: rebased on top of latest CLK codebase drivers/clk/clk-fractional-divider.c | 11 +++++++---- drivers/clk/clk-fractional-divider.h | 9 +++++++++ drivers/clk/rockchip/clk.c | 17 +++-------------- 3 files changed, 19 insertions(+), 18 deletions(-) create mode 100644 drivers/clk/clk-fractional-divider.h diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c index b1e556f20911..535d299af646 100644 --- a/drivers/clk/clk-fractional-divider.c +++ b/drivers/clk/clk-fractional-divider.c @@ -14,6 +14,8 @@ #include #include +#include "clk-fractional-divider.h" + static inline u32 clk_fd_readl(struct clk_fractional_divider *fd) { if (fd->flags & CLK_FRAC_DIVIDER_BIG_ENDIAN) @@ -68,9 +70,10 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw *hw, return ret; } -static void clk_fd_general_approximation(struct clk_hw *hw, unsigned long rate, - unsigned long *parent_rate, - unsigned long *m, unsigned long *n) +void clk_fractional_divider_general_approximation(struct clk_hw *hw, + unsigned long rate, + unsigned long *parent_rate, + unsigned long *m, unsigned long *n) { struct clk_fractional_divider *fd = to_clk_fd(hw); unsigned long scale; @@ -102,7 +105,7 @@ static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate, if (fd->approximation) fd->approximation(hw, rate, parent_rate, &m, &n); else - clk_fd_general_approximation(hw, rate, parent_rate, &m, &n); + clk_fractional_divider_general_approximation(hw, rate, parent_rate, &m, &n); ret = (u64)*parent_rate * m; do_div(ret, n); diff --git a/drivers/clk/clk-fractional-divider.h b/drivers/clk/clk-fractional-divider.h new file mode 100644 index 000000000000..4fa359a12ef4 --- /dev/null +++ b/drivers/clk/clk-fractional-divider.h @@ -0,0 +1,9 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +struct clk_hw; + +void clk_fractional_divider_general_approximation(struct clk_hw *hw, + unsigned long rate, + unsigned long *parent_rate, + unsigned long *m, + unsigned long *n); diff --git a/drivers/clk/rockchip/clk.c b/drivers/clk/rockchip/clk.c index 049e5e0b64f6..b7be7e11b0df 100644 --- a/drivers/clk/rockchip/clk.c +++ b/drivers/clk/rockchip/clk.c @@ -22,6 +22,8 @@ #include #include #include + +#include "../clk-fractional-divider.h" #include "clk.h" /* @@ -178,10 +180,8 @@ static void rockchip_fractional_approximation(struct clk_hw *hw, unsigned long rate, unsigned long *parent_rate, unsigned long *m, unsigned long *n) { - struct clk_fractional_divider *fd = to_clk_fd(hw); unsigned long p_rate, p_parent_rate; struct clk_hw *p_parent; - unsigned long scale; p_rate = clk_hw_get_rate(clk_hw_get_parent(hw)); if ((rate * 20 > p_rate) && (p_rate % rate != 0)) { @@ -190,18 +190,7 @@ static void rockchip_fractional_approximation(struct clk_hw *hw, *parent_rate = p_parent_rate; } - /* - * Get rate closer to *parent_rate to guarantee there is no overflow - * for m and n. In the result it will be the nearest rate left shifted - * by (scale - fd->nwidth) bits. - */ - scale = fls_long(*parent_rate / rate - 1); - if (scale > fd->nwidth) - rate <<= scale - fd->nwidth; - - rational_best_approximation(rate, *parent_rate, - GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0), - m, n); + clk_fractional_divider_general_approximation(hw, rate, parent_rate, m, n); } static struct clk *rockchip_clk_register_frac_branch( From patchwork Thu Aug 12 17:00:23 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Shevchenko X-Patchwork-Id: 496609 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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 1296AC43214 for ; Thu, 12 Aug 2021 17:00:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E2BE0610A3 for ; Thu, 12 Aug 2021 17:00:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234006AbhHLRBK (ORCPT ); Thu, 12 Aug 2021 13:01:10 -0400 Received: from mga17.intel.com ([192.55.52.151]:36933 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233901AbhHLRBJ (ORCPT ); Thu, 12 Aug 2021 13:01:09 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10074"; a="195670090" X-IronPort-AV: E=Sophos;i="5.84,316,1620716400"; d="scan'208";a="195670090" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Aug 2021 10:00:42 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.84,316,1620716400"; d="scan'208";a="503934251" Received: from black.fi.intel.com ([10.237.72.28]) by orsmga001.jf.intel.com with ESMTP; 12 Aug 2021 10:00:30 -0700 Received: by black.fi.intel.com (Postfix, from userid 1003) id 1D23E9F; Thu, 12 Aug 2021 20:00:29 +0300 (EEST) From: Andy Shevchenko To: "Rafael J. Wysocki" , Andy Shevchenko , Heiko Stuebner , Elaine Zhang , Stephen Boyd , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-clk@vger.kernel.org, linux-imx@nxp.com, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org Cc: "Rafael J. Wysocki" , Len Brown , Michael Turquette , Abel Vesa , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Lee Jones Subject: [PATCH v4 2/4] clk: fractional-divider: Hide clk_fractional_divider_ops from wide audience Date: Thu, 12 Aug 2021 20:00:23 +0300 Message-Id: <20210812170025.67074-2-andriy.shevchenko@linux.intel.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com> References: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org The providers are all located in drivers/clk/ and hence no need to export the clock operations to wider audience. Hide them by moving to drivers/clk/clk-fractional-divider.h. Signed-off-by: Andy Shevchenko --- v4: rebased on top of latest CLK codebase, fixed compilation error drivers/clk/clk-fractional-divider.h | 2 ++ drivers/clk/imx/clk-composite-7ulp.c | 1 + include/linux/clk-provider.h | 1 - 3 files changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/clk/clk-fractional-divider.h b/drivers/clk/clk-fractional-divider.h index 4fa359a12ef4..aaaef90b2777 100644 --- a/drivers/clk/clk-fractional-divider.h +++ b/drivers/clk/clk-fractional-divider.h @@ -2,6 +2,8 @@ struct clk_hw; +extern const struct clk_ops clk_fractional_divider_ops; + void clk_fractional_divider_general_approximation(struct clk_hw *hw, unsigned long rate, unsigned long *parent_rate, diff --git a/drivers/clk/imx/clk-composite-7ulp.c b/drivers/clk/imx/clk-composite-7ulp.c index 7c4f31b31eb0..d85ba78abbb1 100644 --- a/drivers/clk/imx/clk-composite-7ulp.c +++ b/drivers/clk/imx/clk-composite-7ulp.c @@ -10,6 +10,7 @@ #include #include +#include "../clk-fractional-divider.h" #include "clk.h" #define PCG_PCS_SHIFT 24 diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h index 7be81d5fcf8c..d8609aef2394 100644 --- a/include/linux/clk-provider.h +++ b/include/linux/clk-provider.h @@ -1023,7 +1023,6 @@ struct clk_fractional_divider { #define CLK_FRAC_DIVIDER_ZERO_BASED BIT(0) #define CLK_FRAC_DIVIDER_BIG_ENDIAN BIT(1) -extern const struct clk_ops clk_fractional_divider_ops; struct clk *clk_register_fractional_divider(struct device *dev, const char *name, const char *parent_name, unsigned long flags, void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth, From patchwork Thu Aug 12 17:00:24 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Shevchenko X-Patchwork-Id: 496610 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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 09B7AC4320A for ; Thu, 12 Aug 2021 17:00:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D5B6560FBF for ; Thu, 12 Aug 2021 17:00:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233823AbhHLRBC (ORCPT ); Thu, 12 Aug 2021 13:01:02 -0400 Received: from mga11.intel.com ([192.55.52.93]:13232 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233728AbhHLRBB (ORCPT ); Thu, 12 Aug 2021 13:01:01 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10074"; a="212287081" X-IronPort-AV: E=Sophos;i="5.84,316,1620716400"; d="scan'208";a="212287081" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Aug 2021 10:00:35 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.84,316,1620716400"; d="scan'208";a="446614409" Received: from black.fi.intel.com ([10.237.72.28]) by fmsmga007.fm.intel.com with ESMTP; 12 Aug 2021 10:00:29 -0700 Received: by black.fi.intel.com (Postfix, from userid 1003) id 2786B1E0; Thu, 12 Aug 2021 20:00:29 +0300 (EEST) From: Andy Shevchenko To: "Rafael J. Wysocki" , Andy Shevchenko , Heiko Stuebner , Elaine Zhang , Stephen Boyd , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-clk@vger.kernel.org, linux-imx@nxp.com, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org Cc: "Rafael J. Wysocki" , Len Brown , Michael Turquette , Abel Vesa , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Lee Jones , Liu Ying Subject: [PATCH v4 3/4] clk: fractional-divider: Introduce POWER_OF_TWO_PS flag Date: Thu, 12 Aug 2021 20:00:24 +0300 Message-Id: <20210812170025.67074-3-andriy.shevchenko@linux.intel.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com> References: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org The newly introduced POWER_OF_TWO_PS flag, when set, makes the flow to skip the assumption that the caller will use an additional 2^scale prescaler to get the desired clock rate. Reported-by: Liu Ying Signed-off-by: Andy Shevchenko --- v4: rebased on top of latest CLK codebase drivers/acpi/acpi_lpss.c | 4 ++-- drivers/clk/clk-fractional-divider.c | 10 ++++++---- drivers/mfd/intel-lpss.c | 3 ++- include/linux/clk-provider.h | 11 +++++++++-- 4 files changed, 19 insertions(+), 9 deletions(-) diff --git a/drivers/acpi/acpi_lpss.c b/drivers/acpi/acpi_lpss.c index 7f163074e4e4..30b1f511c2af 100644 --- a/drivers/acpi/acpi_lpss.c +++ b/drivers/acpi/acpi_lpss.c @@ -436,8 +436,8 @@ static int register_device_clock(struct acpi_device *adev, if (!clk_name) return -ENOMEM; clk = clk_register_fractional_divider(NULL, clk_name, parent, - 0, prv_base, - 1, 15, 16, 15, 0, NULL); + CLK_FRAC_DIVIDER_POWER_OF_TWO_PS, + prv_base, 1, 15, 16, 15, 0, NULL); parent = clk_name; clk_name = kasprintf(GFP_KERNEL, "%s-update", devname); diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c index 535d299af646..6a3ed82fdae9 100644 --- a/drivers/clk/clk-fractional-divider.c +++ b/drivers/clk/clk-fractional-divider.c @@ -76,16 +76,18 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw, unsigned long *m, unsigned long *n) { struct clk_fractional_divider *fd = to_clk_fd(hw); - unsigned long scale; /* * Get rate closer to *parent_rate to guarantee there is no overflow * for m and n. In the result it will be the nearest rate left shifted * by (scale - fd->nwidth) bits. */ - scale = fls_long(*parent_rate / rate - 1); - if (scale > fd->nwidth) - rate <<= scale - fd->nwidth; + if (fd->flags & CLK_FRAC_DIVIDER_POWER_OF_TWO_PS) { + unsigned long scale = fls_long(*parent_rate / rate - 1); + + if (scale > fd->nwidth) + rate <<= scale - fd->nwidth; + } rational_best_approximation(rate, *parent_rate, GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0), diff --git a/drivers/mfd/intel-lpss.c b/drivers/mfd/intel-lpss.c index a9bf10bee796..0e15afc39f54 100644 --- a/drivers/mfd/intel-lpss.c +++ b/drivers/mfd/intel-lpss.c @@ -301,7 +301,8 @@ static int intel_lpss_register_clock_divider(struct intel_lpss *lpss, snprintf(name, sizeof(name), "%s-div", devname); tmp = clk_register_fractional_divider(NULL, name, __clk_get_name(tmp), - 0, lpss->priv, 1, 15, 16, 15, 0, + CLK_FRAC_DIVIDER_POWER_OF_TWO_PS, + lpss->priv, 1, 15, 16, 15, 0, NULL); if (IS_ERR(tmp)) return PTR_ERR(tmp); diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h index d8609aef2394..f59c875271a0 100644 --- a/include/linux/clk-provider.h +++ b/include/linux/clk-provider.h @@ -1001,6 +1001,12 @@ struct clk_hw *devm_clk_hw_register_fixed_factor(struct device *dev, * CLK_FRAC_DIVIDER_BIG_ENDIAN - By default little endian register accesses are * used for the divider register. Setting this flag makes the register * accesses big endian. + * CLK_FRAC_DIVIDER_POWER_OF_TWO_PS - By default the resulting fraction might + * be saturated and the caller will get quite far from the good enough + * approximation. Instead the caller may require, by setting this flag, + * to shift left by a few bits in case, when the asked one is quite small + * to satisfy the desired range of denominator. It assumes that on the + * caller's side the power-of-two capable prescaler exists. */ struct clk_fractional_divider { struct clk_hw hw; @@ -1020,8 +1026,9 @@ struct clk_fractional_divider { #define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw) -#define CLK_FRAC_DIVIDER_ZERO_BASED BIT(0) -#define CLK_FRAC_DIVIDER_BIG_ENDIAN BIT(1) +#define CLK_FRAC_DIVIDER_ZERO_BASED BIT(0) +#define CLK_FRAC_DIVIDER_BIG_ENDIAN BIT(1) +#define CLK_FRAC_DIVIDER_POWER_OF_TWO_PS BIT(2) struct clk *clk_register_fractional_divider(struct device *dev, const char *name, const char *parent_name, unsigned long flags, From patchwork Thu Aug 12 17:00:25 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Shevchenko X-Patchwork-Id: 496082 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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 5F571C4320A for ; Thu, 12 Aug 2021 17:00:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E9456109D for ; Thu, 12 Aug 2021 17:00:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234048AbhHLRBQ (ORCPT ); Thu, 12 Aug 2021 13:01:16 -0400 Received: from mga05.intel.com ([192.55.52.43]:1108 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233901AbhHLRBQ (ORCPT ); Thu, 12 Aug 2021 13:01:16 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10074"; a="300986774" X-IronPort-AV: E=Sophos;i="5.84,316,1620716400"; d="scan'208";a="300986774" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Aug 2021 10:00:38 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.84,316,1620716400"; d="scan'208";a="517527485" Received: from black.fi.intel.com ([10.237.72.28]) by FMSMGA003.fm.intel.com with ESMTP; 12 Aug 2021 10:00:29 -0700 Received: by black.fi.intel.com (Postfix, from userid 1003) id 30EA5238; Thu, 12 Aug 2021 20:00:29 +0300 (EEST) From: Andy Shevchenko To: "Rafael J. Wysocki" , Andy Shevchenko , Heiko Stuebner , Elaine Zhang , Stephen Boyd , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-clk@vger.kernel.org, linux-imx@nxp.com, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org Cc: "Rafael J. Wysocki" , Len Brown , Michael Turquette , Abel Vesa , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Lee Jones , Liu Ying Subject: [PATCH v4 4/4] clk: fractional-divider: Document the arithmetics used behind the code Date: Thu, 12 Aug 2021 20:00:25 +0300 Message-Id: <20210812170025.67074-4-andriy.shevchenko@linux.intel.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com> References: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org It appears that some code lines raise the question why they are needed and how they are participated in the calculus of the resulting values. Document this in a form of the top comment in the module file. Reported-by: Liu Ying Signed-off-by: Andy Shevchenko --- v4: rebased on top of latest CLK codebase drivers/clk/clk-fractional-divider.c | 35 +++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c index 6a3ed82fdae9..b4f365d97bd0 100644 --- a/drivers/clk/clk-fractional-divider.c +++ b/drivers/clk/clk-fractional-divider.c @@ -3,8 +3,39 @@ * Copyright (C) 2014 Intel Corporation * * Adjustable fractional divider clock implementation. - * Output rate = (m / n) * parent_rate. * Uses rational best approximation algorithm. + * + * Output is calculated as + * + * rate = (m / n) * parent_rate (1) + * + * This is useful when on die we have a prescaler block which asks for + * m (numerator) and n (denominator) values to be provided to satisfy + * the (1) as much as possible. + * + * Since m and n have the limitation by a range, e.g. + * + * n >= 1, n < N_width, where N_width = 2^nwidth (2) + * + * for some cases the output may be saturated. Hence, from (1) and (2), + * assuming the worst case when m = 1, the inequality + * + * floor(log2(parent_rate / rate)) <= nwidth (3) + * + * may be derived. Thus, in cases when + * + * (parent_rate / rate) >> N_width (4) + * + * we might scale up the rate by 2^scale (see the description of + * CLK_FRAC_DIVIDER_POWER_OF_TWO_PS for additional information), where + * + * scale = floor(log2(parent_rate / rate)) - nwidth (5) + * + * and assume that the IP, that needs m and n, has also its own + * prescaler, which is capable to divide by 2^scale. In this way + * we get the denominator to satisfy the desired range (2) and + * at the same time much much better result of m and n than simple + * saturated values. */ #include @@ -81,6 +112,8 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw, * Get rate closer to *parent_rate to guarantee there is no overflow * for m and n. In the result it will be the nearest rate left shifted * by (scale - fd->nwidth) bits. + * + * For the detailed explanation see the top comment in this file. */ if (fd->flags & CLK_FRAC_DIVIDER_POWER_OF_TWO_PS) { unsigned long scale = fls_long(*parent_rate / rate - 1);