From patchwork Tue Apr 23 20:15:10 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Martin Sperl X-Patchwork-Id: 10913727 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7ACF41515 for ; Tue, 23 Apr 2019 20:16:36 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6C926288FC for ; Tue, 23 Apr 2019 20:16:36 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 6119C2891A; Tue, 23 Apr 2019 20:16:36 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 1A0EA288FC for ; Tue, 23 Apr 2019 20:16:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:MIME-Version:Cc:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:References: In-Reply-To:Message-Id:Date:Subject:To:From:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=RCW13xe3wVj7L8Md6t80nRlKxz4sM2RibKF0CAW4jMM=; b=PRqeZZFp3mqNoVVX4W4gzBISGE 436LvuqsrCroiH/wAQrAjZZLc3yeMtthDGgbOc1irNsG5SFppmDG31Jm7qINJGdOrYBwzbh35IzqL knzssiVF7W39E0ywup06n3sZnVV55vG/9XBQZ/sWx5UoIL7qISzAjAwXxq4rlPAvBTXld/ldPDXkr EdIVHQlxRsgV/+8BxW2FgOR3fj/EBRim0gq+d2kyhjbXy+8B6LyVP7C9e8pD1oiFKw3pcpicy3Tfq qMpM3X262i8WTY65cT2zsusG9zEXiAcSHubnqNRvbzyzETHymW7eya230O8zFWFlYMP8QeHq67kH0 z3CEydGg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hJ1qA-0000S6-1X; Tue, 23 Apr 2019 20:16:30 +0000 Received: from 212-186-180-163.static.upcbusiness.at ([212.186.180.163] helo=cgate.sperl.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hJ1pd-00086p-Ct; Tue, 23 Apr 2019 20:16:01 +0000 Received: from hc1.intern.sperl.org (account martin@sperl.org [10.10.10.59] verified) by sperl.org (CommuniGate Pro SMTP 6.2.1 _community_) with ESMTPSA id 7763605; Tue, 23 Apr 2019 20:15:33 +0000 From: kernel@martin.sperl.org To: Mark Brown , Eric Anholt , Stefan Wahren , linux-spi@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH V2 3/6] spi: bcm2835: added comment about different bus behaviour of DMA mode Date: Tue, 23 Apr 2019 20:15:10 +0000 Message-Id: <20190423201513.8073-4-kernel@martin.sperl.org> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20190423201513.8073-1-kernel@martin.sperl.org> References: <20190423201513.8073-1-kernel@martin.sperl.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190423_131558_268516_D7451DF1 X-CRM114-Status: UNSURE ( 7.32 ) X-CRM114-Notice: Please train this message. X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Martin Sperl MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP From: Martin Sperl The DMA mode behaves slightly different than polling or interrupt driven mode, so just document the fact Signed-off-by: Martin Sperl Changelog: V1 -> V2: applied feedback by Stefan Wahren new in V2 --- drivers/spi/spi-bcm2835.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) -- 2.11.0 diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c index a64bfa8e0710..3140d952c03a 100644 --- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -828,7 +828,10 @@ static int bcm2835_spi_transfer_one(struct spi_master *master, if (tfr->len < spi_used_hz / HZ_PER_BYTE) return bcm2835_spi_transfer_one_poll(master, spi, tfr, cs); - /* run in dma mode if conditions are right */ + /* run in dma mode if conditions are right + * Note that unlike poll or interrupt mode DMA mode does not have + * this 1 idle clock cycle pattern but runs the spi clock without gaps + */ if (master->can_dma && bcm2835_spi_can_dma(master, spi, tfr)) return bcm2835_spi_transfer_one_dma(master, spi, tfr, cs);