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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6DEEC32793 for ; Wed, 24 Aug 2022 01:30:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229640AbiHXBau (ORCPT ); Tue, 23 Aug 2022 21:30:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48618 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232965AbiHXBar (ORCPT ); Tue, 23 Aug 2022 21:30:47 -0400 X-Greylist: delayed 136 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Tue, 23 Aug 2022 18:30:45 PDT Received: from p3plsmtpa06-01.prod.phx3.secureserver.net (p3plsmtpa06-01.prod.phx3.secureserver.net [173.201.192.102]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BC1821BE97 for ; Tue, 23 Aug 2022 18:30:44 -0700 (PDT) Received: from black ([121.35.128.89]) by :SMTPAUTH: with ESMTPSA id QfBxo3UvK8KflQfBzoFS6c; Tue, 23 Aug 2022 18:28:29 -0700 X-CMAE-Analysis: v=2.4 cv=WdvJ12tX c=1 sm=1 tr=0 ts=63057ebd a=Ts6IU5S7MsxbcnDc+OdCiQ==:117 a=Ts6IU5S7MsxbcnDc+OdCiQ==:17 a=IkcTkHD0fZMA:10 a=NEAV23lmAAAA:8 a=VwQbUJbxAAAA:8 a=_twTT5zqAAAA:8 a=pGLkceISAAAA:8 a=ATfU8fHJlrvmeOZnxusA:9 a=QEXdDO2ut3YA:10 a=AjGcO6oz07-iQ99wixmX:22 a=ILoXdGDbYT3DTB7Z0gVI:22 X-SECURESERVER-ACCT: dhu@hodcarrier.org Date: Wed, 24 Aug 2022 09:28:25 +0800 From: Du Huanpeng To: Sean Anderson Cc: linux-mips@vger.kernel.org, linux-clk@vger.kernel.org, Yang Ling , linux-kernel@vger.kernel.org, Kelvin Cheung , Stephen Boyd Subject: Re: [RESEND PATCH] clk: ls1c: Fix PLL rate calculation Message-ID: <20220824012825.GA2956@black> References: <20220823033414.198525-1-seanga2@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220823033414.198525-1-seanga2@gmail.com> X-CMAE-Envelope: MS4xfB7Qh1/JJak2gztQXiYgXTUVMZsO1KSPSanPLPhuJCyRNNIvHZpItw6k8A1HpaGJ2vq9orllLlr7Kh7lh85IQK47meW/+e3/Do+4DgYrkECkZeFgsSD1 n5SGWQdhCBGejZWA2Uab7HIcjO6kgYAufbUq+JtB95WoogF8GYjxYiRt0TJDV8VS41n12PtIe/QTVoi9nB+vuiG81U4moMcnh/q0AvPuKaxaXg+MKqAqnFPR JloMvp8VsjCXD6+9WO0BFKRxOiwqVZfpKjOSYLSMaQxZVTvn6WOC5vZZ10illBB8eeBd99M25IKEqJz7k1qAnHpzy7iDdHsogxEQmCSUNKhmEbgJB/R54ar+ ABfLLY0/J+neyz1N2ulop7IPzuFk25+EDqLwDBxh3HVcSpPfJj8= Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Mon, Aug 22, 2022 at 11:34:14PM -0400, Sean Anderson wrote: Dear Sean, > While reviewing Dhu's patch adding ls1c300 clock support to U-Boot [1], I > noticed the following calculation, which is copied from I didn't copy it from this driver, I read the document and ``try'' to understand it. I also write a excel [1] file to calculate values for clock nodes. [1] https://github.com/hodcarrier/ls1c300_bsp > drivers/clk/loongson1/clk-loongson1c.c: > > ulong ls1c300_pll_get_rate(struct clk *clk) > { > unsigned int mult; > long long parent_rate; > void *base; > unsigned int val; > > parent_rate = clk_get_parent_rate(clk); > base = (void *)clk->data; > > val = readl(base + START_FREQ); > mult = FIELD_GET(FRAC_N, val) + FIELD_GET(M_PLL, val); > return (mult * parent_rate) / 4; > } > > I would like to examine the use of M_PLL and FRAC_N to calculate the multiplier > for the PLL. The datasheet has the following to say: > > START_FREQ 位 缺省值 描述 > ========== ===== =========== ==================================== > FRAC_N 23:16 0 PLL 倍频系数的小数部分 > > 由 PLL 倍频系数的整数部分 > M_PLL 15:8 NAND_D[3:0] (理论可以达到 255，建议不要超过 100) > 配置 > > which according to google translate means > > START_FREQ Bits Default Description > ========== ===== ============= ================================================ > FRAC_N 23:16 0 Fractional part of the PLL multiplication factor > > Depends on Integer part of PLL multiplication factor > M_PLL 15:8 NAND_D[3:0] (Theoretically it can reach 255, [but] it is > configuration recommended not to exceed 100) > > So just based on this description, I would expect that the formula to be > something like > > rate = parent * (256 * M_PLL + FRAC_N) / 256 / 4 > > However, the datasheet also gives the following formula: > > rate = parent * (M_PLL + FRAC_N) / 4 > > which is what the Linux driver has implemented. I find this very unusual. > First, the datasheet specifically says that these fields are the integer and > fractional parts of the multiplier. Second, I think such a construct does not > easily map to traditional PLL building blocks. Implementing this formula in > hardware would likely require an adder, just to then set the threshold of a > clock divider. > > I think it is much more likely that the first formula is correct. The author of > the datasheet may think of a multiplier of (say) 3.14 as > > M_PLL = 3 > FRAC_N = 0.14 > > which together sum to the correct multiplier, even though the actual value > stored in FRAC_N would be 36. > > I suspect that this has slipped by unnoticed because when FRAC_N is 0, there is > no difference in the formulae. The following patch is untested, but I suspect > it will fix this issue. I would appreciate if anyone with access to the > hardware could measure the output of the PLL (or one of its derived clocks) and > determine the correct formula. > > [1] https://lore.kernel.org/u-boot/20220418204519.19991-1-dhu@hodcarrier.org/T/#u > > Fixes: b4626a7f4892 ("CLK: Add Loongson1C clock support") > Signed-off-by: Sean Anderson > --- > > drivers/clk/loongson1/clk-loongson1c.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/clk/loongson1/clk-loongson1c.c b/drivers/clk/loongson1/clk-loongson1c.c > index 1ebf740380ef..2aa839b05d6b 100644 > --- a/drivers/clk/loongson1/clk-loongson1c.c > +++ b/drivers/clk/loongson1/clk-loongson1c.c > @@ -21,9 +21,9 @@ static unsigned long ls1x_pll_recalc_rate(struct clk_hw *hw, > u32 pll, rate; > > pll = __raw_readl(LS1X_CLK_PLL_FREQ); > - rate = ((pll >> 8) & 0xff) + ((pll >> 16) & 0xff); > + rate = (pll & 0xff00) + ((pll >> 16) & 0xff); > rate *= OSC; > - rate >>= 2; > + rate >>= 10; > > return rate; > } > -- > 2.37.1 >