From patchwork Tue Sep 27 11:57:03 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Noralf_Tr=C3=B8nnes?= X-Patchwork-Id: 9351777 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id A39826077B for ; Tue, 27 Sep 2016 12:03:20 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 93E32291B2 for ; Tue, 27 Sep 2016 12:03:20 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 8888A291BA; Tue, 27 Sep 2016 12:03:20 +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=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 15FA5291B9 for ; Tue, 27 Sep 2016 12:03:16 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.85_2 #1 (Red Hat Linux)) id 1bor4i-0005FA-TZ; Tue, 27 Sep 2016 12:01:28 +0000 Received: from smtp.domeneshop.no ([2a01:5b40:0:3005::1]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bor1d-0002Cg-W5; Tue, 27 Sep 2016 11:58:24 +0000 Received: from 211.81-166-168.customer.lyse.net ([81.166.168.211]:34833 helo=localhost.localdomain) by smtp.domeneshop.no with esmtpsa (TLS1.1:DHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1bor1D-0005in-3U; Tue, 27 Sep 2016 13:57:51 +0200 From: =?UTF-8?q?Noralf=20Tr=C3=B8nnes?= To: wsa@the-dreams.de, swarren@wwwdotorg.org, eric@anholt.net Subject: [PATCH v2 5/8] i2c: bcm2835: Add support for Repeated Start Condition Date: Tue, 27 Sep 2016 13:57:03 +0200 Message-Id: <1474977426-3272-6-git-send-email-noralf@tronnes.org> X-Mailer: git-send-email 2.8.2 In-Reply-To: <1474977426-3272-1-git-send-email-noralf@tronnes.org> References: <1474977426-3272-1-git-send-email-noralf@tronnes.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20160927_045818_412105_FBEF9FEA X-CRM114-Status: GOOD ( 20.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-rpi-kernel@lists.infradead.org, =?UTF-8?q?Noralf=20Tr=C3=B8nnes?= , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-i2c@vger.kernel.org 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 Documentation/i2c/i2c-protocol states that Combined transactions should separate messages with a Start bit and end the whole transaction with a Stop bit. This patch adds support for issuing only a Start between messages instead of a Stop followed by a Start. This implementation differs from downstream i2c-bcm2708 in 2 respects: - it uses an interrupt to detect that the transfer is active instead of using polling. There is no interrupt for Transfer Active, but by not prefilling the FIFO it's possible to use the TXW interrupt. - when resetting/disabling the controller between transfers it writes CLEAR to the control register instead of just zero. Using just zero gave many errors. This might be the reason why downstream had to disable this feature and make it available with a module parameter. I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel) and AT24C32 (eeprom) in parallel without problems. Signed-off-by: Noralf Trønnes --- drivers/i2c/busses/i2c-bcm2835.c | 101 ++++++++++++++++++++++++--------------- 1 file changed, 63 insertions(+), 38 deletions(-) diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c index 4e08add..f3a1472 100644 --- a/drivers/i2c/busses/i2c-bcm2835.c +++ b/drivers/i2c/busses/i2c-bcm2835.c @@ -63,6 +63,7 @@ struct bcm2835_i2c_dev { struct i2c_adapter adapter; struct completion completion; struct i2c_msg *curr_msg; + int num_msgs; u32 msg_err; u8 *msg_buf; size_t msg_buf_remaining; @@ -109,6 +110,45 @@ static void bcm2835_drain_rxfifo(struct bcm2835_i2c_dev *i2c_dev) } } +/* + * Repeated Start Condition (Sr) + * The BCM2835 ARM Peripherals datasheet mentions a way to trigger a Sr when it + * talks about reading from a slave with 10 bit address. This is achieved by + * issuing a write, poll the I2CS.TA flag and wait for it to be set, and then + * issue a read. + * A comment in https://github.com/raspberrypi/linux/issues/254 shows how the + * firmware actually does it using polling and says that it's a workaround for + * a problem in the state machine. + * It turns out that it is possible to use the TXW interrupt to know when the + * transfer is active, provided the FIFO has not been prefilled. + */ + +static void bcm2835_i2c_start_transfer(struct bcm2835_i2c_dev *i2c_dev) +{ + u32 c = BCM2835_I2C_C_ST | BCM2835_I2C_C_I2CEN; + struct i2c_msg *msg = i2c_dev->curr_msg; + bool last_msg = (i2c_dev->num_msgs == 1); + + if (!i2c_dev->num_msgs) + return; + + i2c_dev->num_msgs--; + i2c_dev->msg_buf = msg->buf; + i2c_dev->msg_buf_remaining = msg->len; + + if (msg->flags & I2C_M_RD) + c |= BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR; + else + c |= BCM2835_I2C_C_INTT; + + if (last_msg) + c |= BCM2835_I2C_C_INTD; + + bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_A, msg->addr); + bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DLEN, msg->len); + bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c); +} + static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data) { struct bcm2835_i2c_dev *i2c_dev = data; @@ -142,6 +182,12 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data) } bcm2835_fill_txfifo(i2c_dev); + + if (i2c_dev->num_msgs && !i2c_dev->msg_buf_remaining) { + i2c_dev->curr_msg++; + bcm2835_i2c_start_transfer(i2c_dev); + } + return IRQ_HANDLED; } @@ -166,30 +212,25 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data) return IRQ_HANDLED; } -static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev, - struct i2c_msg *msg) +static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], + int num) { - u32 c; + struct bcm2835_i2c_dev *i2c_dev = i2c_get_adapdata(adap); unsigned long time_left; + int i; - i2c_dev->curr_msg = msg; - i2c_dev->msg_buf = msg->buf; - i2c_dev->msg_buf_remaining = msg->len; - reinit_completion(&i2c_dev->completion); - - bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR); + for (i = 0; i < (num - 1); i++) + if (msgs[i].flags & I2C_M_RD) { + dev_warn_once(i2c_dev->dev, + "only one read message supported, has to be last\n"); + return -EOPNOTSUPP; + } - if (msg->flags & I2C_M_RD) { - c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR; - } else { - c = BCM2835_I2C_C_INTT; - bcm2835_fill_txfifo(i2c_dev); - } - c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD | BCM2835_I2C_C_I2CEN; + i2c_dev->curr_msg = msgs; + i2c_dev->num_msgs = num; + reinit_completion(&i2c_dev->completion); - bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_A, msg->addr); - bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DLEN, msg->len); - bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c); + bcm2835_i2c_start_transfer(i2c_dev); time_left = wait_for_completion_timeout(&i2c_dev->completion, BCM2835_I2C_TIMEOUT); @@ -200,32 +241,16 @@ static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev, return -ETIMEDOUT; } - if (likely(!i2c_dev->msg_err)) - return 0; + if (!i2c_dev->msg_err) + return num; dev_err_ratelimited(i2c_dev->dev, "i2c transfer failed: %x\n", i2c_dev->msg_err); if (i2c_dev->msg_err & BCM2835_I2C_S_ERR) return -EREMOTEIO; - else - return -EIO; -} - -static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], - int num) -{ - struct bcm2835_i2c_dev *i2c_dev = i2c_get_adapdata(adap); - int i; - int ret = 0; - - for (i = 0; i < num; i++) { - ret = bcm2835_i2c_xfer_msg(i2c_dev, &msgs[i]); - if (ret) - break; - } - return ret ?: i; + return -EIO; } static u32 bcm2835_i2c_func(struct i2c_adapter *adap)