From patchwork Wed Mar 27 20:38:52 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Grant Grundler X-Patchwork-Id: 2353121 Return-Path: X-Original-To: patchwork-linux-mmc@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id 2A95BDFE82 for ; Wed, 27 Mar 2013 20:39:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751980Ab3C0UjM (ORCPT ); Wed, 27 Mar 2013 16:39:12 -0400 Received: from mail-pb0-f52.google.com ([209.85.160.52]:52293 "EHLO mail-pb0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751978Ab3C0UjL (ORCPT ); Wed, 27 Mar 2013 16:39:11 -0400 Received: by mail-pb0-f52.google.com with SMTP id ma3so5464435pbc.39 for ; Wed, 27 Mar 2013 13:39:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=x-received:from:to:cc:subject:date:message-id:x-mailer; bh=0XmXh/ETrD1qUuzkoAuB7/VcG+yRfe+YTNNv6GQ4MRo=; b=ANSO4JvGHOqWkCx6D7vFYC49Fl+B6dMNFvccHiGlfBaCL9gCRUAbqbz+zcIu5AjDT5 CF43nnv00UnidtR7LZ05C9ZeIbYhBqPPbzTqq96LGcAK/N/jfcg12GrlNjRuX30tPeQK DVPBy5k/39Afsit9o23/V0Pkx+8EOj8qz61YY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-received:from:to:cc:subject:date:message-id:x-mailer :x-gm-message-state; bh=0XmXh/ETrD1qUuzkoAuB7/VcG+yRfe+YTNNv6GQ4MRo=; b=gekEzQI/0IzEs2nC2l9dUbXlyNmRJHVlOI5FB4mVRCWr+Fh0gyyagyfDYhy3+Xr5Lz xR30W3Zkn07OES6SBqdPet6DLnVJHAWAgRKgtDcorivp8hG+0d7QxKAqDNTID8goOJzV h5WFkUe5cXwJVTzlwW3wxreI+GNOelPT1FFwauQ7Lw4FG67v+jvNhyN7q0FJeUiQdxkd ZHhcmo3zdIbnTgy0Fraoo3dgihLwB8B6ztn4N1jU1Xxapuwie4rcevhqaeGVwcif5TxG QlKDi29B3G/xR1k7MUm7vhWtbkPltodFJCqaO24BBLuuGDABGOYB+rhysOAzMOn9n6f6 BJmw== X-Received: by 10.66.144.69 with SMTP id sk5mr32792267pab.69.1364416750302; Wed, 27 Mar 2013 13:39:10 -0700 (PDT) Received: from firesword.mtv.corp.google.com (firesword.mtv.corp.google.com [172.22.73.90]) by mx.google.com with ESMTPS id mz8sm22657523pbc.9.2013.03.27.13.39.08 (version=TLSv1.1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 27 Mar 2013 13:39:09 -0700 (PDT) From: Grant Grundler To: Chris Ball Cc: Doug Anderson , Will Newton , Seungwon Jeon , Bing Zhao , Jaehoon Chung , Ashok Nagarajan , Olof Johansson , linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org, Grant Grundler Subject: [PATCH V2] mmc: dw_mmc: rewrite CLKDIV computation Date: Wed, 27 Mar 2013 13:38:52 -0700 Message-Id: <1364416732-23722-1-git-send-email-grundler@chromium.org> X-Mailer: git-send-email 1.8.1.3 X-Gm-Message-State: ALoCoQnyvPw8mRl+8NToGZrAJL5tBhtKvQWDL7JFzx5JOP6sYagqE+SVZ2w2E9o/XTQCMXyCPOny Sender: linux-mmc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mmc@vger.kernel.org When backporting Commit e419990b5e8 ("mmc: dw_mmc: correct the calculation for CLKDIV") to 3.4 kernel and debugging a FW issue, I found the code unreadable. This rewrite simplifies the computation and explains each step. Signed-off-by: Grant Grundler --- V2: rewrote commit msg per feedback Tested on Samsung Series 3 Chromebook (exynos 5250 chipset) using ChromeOS 3.4 kernel (not 3.9-rc3 which this patch is based against). I've posted the test_dw_mmc.c source to confirm this patch generates the same correct values. The CLKDIV issue I was trying to resolve in ChromeOS 3.4 kernel: http://crbug.com/221828 drivers/mmc/host/dw_mmc.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c index 9834221..6fdf55b 100644 --- a/drivers/mmc/host/dw_mmc.c +++ b/drivers/mmc/host/dw_mmc.c @@ -631,14 +631,22 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit) if (slot->clock != host->current_speed || force_clkinit) { div = host->bus_hz / slot->clock; - if (host->bus_hz % slot->clock && host->bus_hz > slot->clock) - /* - * move the + 1 after the divide to prevent - * over-clocking the card. + if (host->bus_hz > slot->clock) { + /* don't overclock due to integer math losses */ + if ((div * slot->clock) < host->bus_hz) + div++; + + /* don't overclock due to resolution of HW */ + if (div & 1) + div++; + + /* See 6.2.3 CLKDIV in "Mobile Storage Host Databook" + * Look for dwc_mobile_storage_db.pdf from Synopsys. + * CLKDIV value 0 means divisor 1, val 1 -> 2, ... */ - div += 1; - - div = (host->bus_hz != slot->clock) ? DIV_ROUND_UP(div, 2) : 0; + div /= 2; + } else + div = 0; /* use bus_hz */ dev_info(&slot->mmc->class_dev, "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ"