From patchwork Tue Jun 21 17:57:19 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vijaya Krishna Nivarthi X-Patchwork-Id: 583803 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 DD362C43334 for ; Tue, 21 Jun 2022 17:57:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241663AbiFUR5n (ORCPT ); Tue, 21 Jun 2022 13:57:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233529AbiFUR5m (ORCPT ); Tue, 21 Jun 2022 13:57:42 -0400 Received: from alexa-out.qualcomm.com (alexa-out.qualcomm.com [129.46.98.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B2301D0D9; Tue, 21 Jun 2022 10:57:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1655834261; x=1687370261; h=from:to:cc:subject:date:message-id; bh=IhpY0nvaFsgCuREHN0wAidroPYiiZ/Yc0RCBikSIN8s=; b=etvoddiJDCTrhIgWEkaNs69M+e61z8BxA4yNlEYGTGp1tdhTk4l7azNy OTGtZwsxR0xjJ49yqOn+l9foW2+rm/It25w4wlEneTeInRlQUEJWnemnJ dP/RQF70ip8yt/4ILOG2swgaZW0/YX/ah9gFr0GP9YdJIilMw9vG3Q61z Y=; Received: from ironmsg07-lv.qualcomm.com ([10.47.202.151]) by alexa-out.qualcomm.com with ESMTP; 21 Jun 2022 10:57:41 -0700 X-QCInternal: smtphost Received: from ironmsg02-blr.qualcomm.com ([10.86.208.131]) by ironmsg07-lv.qualcomm.com with ESMTP/TLS/AES256-SHA; 21 Jun 2022 10:57:39 -0700 X-QCInternal: smtphost Received: from hu-vnivarth-hyd.qualcomm.com (HELO hu-sgudaval-hyd.qualcomm.com) ([10.213.111.166]) by ironmsg02-blr.qualcomm.com with ESMTP; 21 Jun 2022 23:27:24 +0530 Received: by hu-sgudaval-hyd.qualcomm.com (Postfix, from userid 3994820) id 641833FF1; Tue, 21 Jun 2022 23:27:23 +0530 (+0530) From: Vijaya Krishna Nivarthi To: agross@kernel.org, bjorn.andersson@linaro.org, gregkh@linuxfoundation.org, jirislaby@kernel.org, linux-arm-msm@vger.kernel.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Cc: quic_msavaliy@quicinc.com, dianders@chromium.org, mka@chromium.org, swboyd@chromium.org, Vijaya Krishna Nivarthi Subject: [PATCH] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which otherwise could return a sub-optimal clock rate. Date: Tue, 21 Jun 2022 23:27:19 +0530 Message-Id: <1655834239-20812-1-git-send-email-quic_vnivarth@quicinc.com> X-Mailer: git-send-email 2.7.4 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org In the logic around call to clk_round_rate, for some corner conditions, get_clk_div_rate() could return an sub-optimal clock rate. Also, if an exact clock rate was not found lowest clock was being returned. Search for suitable clock rate in 2 steps a) exact match or within 2% tolerance b) within 5% tolerance This also takes care of corner conditions. Fixes: c2194bc999d4 ("tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate") Signed-off-by: Vijaya Krishna Nivarthi Reported-by: kernel test robot Reported-by: kernel test robot --- drivers/tty/serial/qcom_geni_serial.c | 134 ++++++++++++++++++++++++++-------- 1 file changed, 102 insertions(+), 32 deletions(-) diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c index 2e23b65..8d247c1 100644 --- a/drivers/tty/serial/qcom_geni_serial.c +++ b/drivers/tty/serial/qcom_geni_serial.c @@ -943,52 +943,123 @@ static int qcom_geni_serial_startup(struct uart_port *uport) return 0; } -static unsigned long get_clk_div_rate(struct clk *clk, unsigned int baud, - unsigned int sampling_rate, unsigned int *clk_div) +static unsigned long find_clk_rate_in_tol(struct clk *clk, unsigned int desired_clk, + unsigned int *clk_div, unsigned int percent_tol, bool *exact_match) { + unsigned long freq; + unsigned long div, maxdiv, new_div; + unsigned long long mult; unsigned long ser_clk; - unsigned long desired_clk; - unsigned long freq, prev; - unsigned long div, maxdiv; - int64_t mult; - - desired_clk = baud * sampling_rate; - if (!desired_clk) { - pr_err("%s: Invalid frequency\n", __func__); - return 0; - } + unsigned long test_freq, offset, new_freq; + ser_clk = 0; maxdiv = CLK_DIV_MSK >> CLK_DIV_SHFT; - prev = 0; + div = 1; - for (div = 1; div <= maxdiv; div++) { - mult = div * desired_clk; - if (mult > ULONG_MAX) + while (div <= maxdiv) { + mult = (unsigned long long)div * desired_clk; + if (mult != (unsigned long)mult) break; - freq = clk_round_rate(clk, (unsigned long)mult); - if (!(freq % desired_clk)) { - ser_clk = freq; - break; + /* + * Loop requesting a freq within tolerance and possibly exact freq. + * + * We'll keep track of the lowest freq inexact match we found + * but always try to find a perfect match. NOTE: this algorithm + * could miss a slightly better freq if there's more than one + * freq between (freq - offset) and (freq) but (freq) can't be made + * exactly, but that's OK. + * + * This absolutely relies on the fact that the Qualcomm clock + * driver always rounds up. + * We make use of exact_match as an I/O param. + */ + + /* look only for exact match if within tolerance is already found */ + if (ser_clk) + offset = 0; + else + offset = (mult * percent_tol) / 100; + + test_freq = mult - offset; + freq = clk_round_rate(clk, test_freq); + + /* + * A dead-on freq is an insta-win, look for it only in 1st run + */ + if (*exact_match) { + if (!(freq % desired_clk)) { + ser_clk = freq; + *clk_div = freq / desired_clk; + return ser_clk; + } + } + + if (!ser_clk) { + new_div = DIV_ROUND_CLOSEST(freq, desired_clk); + new_freq = new_div * desired_clk; + offset = (new_freq * percent_tol) / 100; + + if (new_freq - offset <= freq && freq <= new_freq + offset) { + /* Save the first (lowest freq) within tolerance */ + ser_clk = freq; + *clk_div = new_div; + /* no more search for exact match required in 2nd run */ + if (!(*exact_match)) + break; + } } - if (!prev) - ser_clk = freq; - else if (prev == freq) + div = freq / desired_clk + 1; + + /* + * Only time clock framework doesn't round up is if + * we're past the max clock rate. We're done searching + * if that's the case. + */ + if (freq < test_freq) break; + } + + *exact_match = false; + return ser_clk; +} + +static unsigned long get_clk_div_rate(struct clk *clk, unsigned int baud, + unsigned int sampling_rate, unsigned int *clk_div) +{ + unsigned long ser_clk; + unsigned long desired_clk; + unsigned long desired_tol; + bool exact_match; - prev = freq; + desired_clk = baud * sampling_rate; + if (!desired_clk) { + pr_err("%s: Invalid frequency\n", __func__); + return 0; } - if (!ser_clk) { - pr_err("%s: Can't find matching DFS entry for baud %d\n", - __func__, baud); + /* try to find exact clock rate or within 2% tolerance */ + ser_clk = 0; + exact_match = true; + desired_tol = 2; + + ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, desired_tol, &exact_match); + if (ser_clk) { + if (!exact_match) + pr_warn("Cannot find exact match clk_rate, using one within 2 percent tolerance\n"); return ser_clk; } - *clk_div = ser_clk / desired_clk; - if (!(*clk_div)) - *clk_div = 1; + /* try within 5% tolerance now, no need to look for exact match */ + exact_match = false; + desired_tol = 5; + + ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, desired_tol, &exact_match); + if (ser_clk) + pr_warn("Cannot find exact match clk_rate, using one within 5 percent tolerance\n"); + else + pr_err("Cannot find suitable clk_rate, giving up\n"); return ser_clk; } @@ -1021,8 +1092,7 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport, if (ver >= QUP_SE_VERSION_2_5) sampling_rate /= 2; - clk_rate = get_clk_div_rate(port->se.clk, baud, - sampling_rate, &clk_div); + clk_rate = get_clk_div_rate(port->se.clk, baud, sampling_rate, &clk_div); if (!clk_rate) goto out_restart_rx;