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 X-Spam-Level: X-Spam-Status: No, score=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_GIT autolearn=ham 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 C0C45C43381 for ; Mon, 18 Mar 2019 07:34:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 913122085A for ; Mon, 18 Mar 2019 07:34:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1552894464; bh=NR5fA426N6ri7El5Amha0pSFo/RnlLKqNKjOwMAKwrs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=N4ioslcqnJtGblP65fnM8lkpLnO1hQNFj28ECNf9L1oDbNkkqNDljtvr7d5aSON/A WKVdYiZFrcVf6RWAGjeCT9l4JVZVIz0qdg7ezQa/4VXrqUyiOw+2StzSLgQLNQDAlq 36MP3NyD1JVexhc3cAmXmAbh7BGjWj2fjsxhoVtw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727469AbfCRHeT (ORCPT ); Mon, 18 Mar 2019 03:34:19 -0400 Received: from mirror2.csie.ntu.edu.tw ([140.112.30.76]:40894 "EHLO wens.csie.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726846AbfCRHeO (ORCPT ); Mon, 18 Mar 2019 03:34:14 -0400 Received: by wens.csie.org (Postfix, from userid 1000) id F3F3C5FD69; Mon, 18 Mar 2019 15:34:11 +0800 (CST) From: Chen-Yu Tsai To: Srinivas Kandagatla , Maxime Ripard Cc: linux-sunxi@googlegroups.com, Chen-Yu Tsai , linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/6] nvmem: sunxi_sid: Optimize register read-out method Date: Mon, 18 Mar 2019 15:33:50 +0800 Message-Id: <20190318073354.12151-3-wens@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190318073354.12151-1-wens@kernel.org> References: <20190318073354.12151-1-wens@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Chen-Yu Tsai SID cells are 32-bit aligned, and a multiple of 32 bits in length. The only outlier is the thermal sensor calibration data, which is 16 bits per sensor. However a whole 64 bits is allocated for this purpose, so we could consider it conforming to the rule above. Also, the register read-out method assumes native endian, unlike the direct MMIO method, which assumes big endian. Thus no endian conversion is involved. Under these assumptions, the register read-out method can be slightly optimized. Instead of reading one word then discarding 3 bytes, read the whole word directly into the buffer. However, for reads under 4 bytes or trailing bytes, we still use a scratch buffer to extract the requested bytes. We could go one step further if .word_size was 4, but changing that would affect the sysfs interface's behavior. Signed-off-by: Chen-Yu Tsai --- drivers/nvmem/sunxi_sid.c | 38 ++++++++++++++++++-------------------- 1 file changed, 18 insertions(+), 20 deletions(-) diff --git a/drivers/nvmem/sunxi_sid.c b/drivers/nvmem/sunxi_sid.c index 704c35edf796..15fbfab62595 100644 --- a/drivers/nvmem/sunxi_sid.c +++ b/drivers/nvmem/sunxi_sid.c @@ -115,36 +115,34 @@ static int sun8i_sid_register_readout(const struct sunxi_sid *sid, * to be not reliable at all. * Read by the registers instead. */ -static int sun8i_sid_read_byte_by_reg(const struct sunxi_sid *sid, - const unsigned int offset, - u8 *out) -{ - u32 word; - int ret; - - ret = sun8i_sid_register_readout(sid, offset & ~0x03, &word); - - if (ret) - return ret; - - *out = (word >> ((offset & 0x3) * 8)) & 0xff; - - return 0; -} - static int sun8i_sid_read_by_reg(void *context, unsigned int offset, void *val, size_t bytes) { struct sunxi_sid *sid = context; - u8 *buf = val; + u32 word; int ret; - while (bytes--) { - ret = sun8i_sid_read_byte_by_reg(sid, offset++, buf++); + /* .stride = 4 so offset is guaranteed to be aligned */ + while (bytes >= 4) { + ret = sun8i_sid_register_readout(sid, offset, val); if (ret) return ret; + + val += 4; + offset += 4; + bytes -= 4; } + if (!bytes) + return 0; + + /* Handle any trailing bytes */ + ret = sun8i_sid_register_readout(sid, offset, &word); + if (ret) + return ret; + + memcpy(val, &word, bytes); + return 0; } -- 2.20.1