From: "Noralf Trønnes" <noralf@tronnes.org>
To: wsa@the-dreams.de, swarren@wwwdotorg.org, eric@anholt.net
Cc: linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-rpi-kernel@lists.infradead.org,
"Noralf Trønnes" <noralf@tronnes.org>
Subject: [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer
Date: Mon, 19 Sep 2016 17:26:16 +0200 [thread overview]
Message-ID: <1474298777-5858-2-git-send-email-noralf@tronnes.org> (raw)
In-Reply-To: <1474298777-5858-1-git-send-email-noralf@tronnes.org>
Some SMBus protocols use Repeated Start Condition to switch from write
mode to read mode. Devices like MMA8451 won't work without it.
When downstream implemented support for this in i2c-bcm2708, it broke
support for some devices, so a module parameter was added and combined
transfer was disabled by default.
See https://github.com/raspberrypi/linux/issues/599
It doesn't seem to have been any investigation into what the problem
really was. Later there was added a timeout on the polling loop.
One of the devices mentioned to partially stop working was DS1307.
I have run thousands of transfers to a DS1307 (rtc), MMA8451 (accel)
and AT24C32 (eeprom) in parallel without problems.
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
---
drivers/i2c/busses/i2c-bcm2835.c | 107 +++++++++++++++++++++++++++++++++++----
1 file changed, 98 insertions(+), 9 deletions(-)
diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index f283b71..b3ce565 100644
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -154,8 +154,39 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
return IRQ_NONE;
}
+/*
+ * 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 (without enabling interrupts), poll the I2CS.TA flag and
+ * wait for it to be set, and then issue a read.
+ * https://github.com/raspberrypi/linux/issues/254 shows how the firmware does
+ * it and states that it's a workaround for a problem in the state machine.
+ * This is the comment in the firmware code:
+ *
+ * The I2C peripheral samples the values for rw_bit and xfer_count in the
+ * IDLE state if start is set.
+ *
+ * We want to generate a ReSTART not a STOP at the end of the TX phase. In
+ * order to do that we must ensure the state machine goes
+ * RACK1 -> RACK2 -> SRSTRT1 (not RACK1 -> RACK2 -> SSTOP1).
+ *
+ * So, in the RACK2 state when (TX) xfer_count==0 we must therefore have
+ * already set, ready to be sampled:
+ * READ; rw_bit <= I2CC bit 0 - must be "read"
+ * ST; start <= I2CC bit 7 - must be "Go" in order to not issue STOP
+ * DLEN; xfer_count <= I2CDLEN - must be equal to our read amount
+ *
+ * The plan to do this is:
+ * 1. Start the sub-address write, but don't let it finish (keep
+ * xfer_count > 0)
+ * 2. Populate READ, DLEN and ST in preparation for ReSTART read sequence
+ * 3. Let TX finish (write the rest of the data)
+ * 4. Read back data as it arrives
+ */
+
static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev,
- struct i2c_msg *msg)
+ struct i2c_msg *msg, struct i2c_msg *msg2)
{
u32 c;
unsigned long time_left;
@@ -167,21 +198,70 @@ static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev,
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
- if (msg->flags & I2C_M_RD) {
- c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
- } else {
- c = BCM2835_I2C_C_INTT;
+ if (!(msg->flags & I2C_M_RD))
bcm2835_fill_txfifo(i2c_dev);
- }
- c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD | BCM2835_I2C_C_I2CEN;
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);
+
+ if (!msg2) {
+ if (msg->flags & I2C_M_RD)
+ c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR;
+ else
+ c = BCM2835_I2C_C_INTT;
+
+ c |= BCM2835_I2C_C_ST | BCM2835_I2C_C_INTD |
+ BCM2835_I2C_C_I2CEN;
+ bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+ } else {
+ unsigned long flags;
+ u32 stat, err = 0;
+
+ local_irq_save(flags);
+
+ /* Start write message */
+ c = BCM2835_I2C_C_ST | BCM2835_I2C_C_I2CEN;
+ bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+
+ /* Wait for the transfer to become active */
+ for (time_left = 100; time_left > 0; time_left--) {
+ stat = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
+
+ err = stat & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);
+ if (err)
+ break;
+
+ if (stat & BCM2835_I2C_S_TA)
+ break;
+ }
+
+ if (err || !time_left) {
+ i2c_dev->msg_err = err;
+ local_irq_restore(flags);
+ goto error;
+ }
+
+ /* Start read message */
+ i2c_dev->curr_msg = msg2;
+ i2c_dev->msg_buf = msg2->buf;
+ i2c_dev->msg_buf_remaining = msg2->len;
+ bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_DLEN, msg2->len);
+
+ c = BCM2835_I2C_C_READ | BCM2835_I2C_C_INTR |
+ BCM2835_I2C_C_INTD | BCM2835_I2C_C_ST |
+ BCM2835_I2C_C_I2CEN;
+
+ bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
+
+ local_irq_restore(flags);
+ }
time_left = wait_for_completion_timeout(&i2c_dev->completion,
BCM2835_I2C_TIMEOUT);
+error:
bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, BCM2835_I2C_C_CLEAR);
+ bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_S, BCM2835_I2C_S_CLKT |
+ BCM2835_I2C_S_ERR | BCM2835_I2C_S_DONE);
if (!time_left) {
dev_err(i2c_dev->dev, "i2c transfer timed out\n");
return -ETIMEDOUT;
@@ -209,8 +289,17 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
int i;
int ret = 0;
+ /* Combined write-read to the same address (smbus) */
+ if (num == 2 && (msgs[0].addr == msgs[1].addr) &&
+ !(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
+ (msgs[0].len <= 16)) {
+ ret = bcm2835_i2c_xfer_msg(i2c_dev, &msgs[0], &msgs[1]);
+
+ return ret ? ret : 2;
+ }
+
for (i = 0; i < num; i++) {
- ret = bcm2835_i2c_xfer_msg(i2c_dev, &msgs[i]);
+ ret = bcm2835_i2c_xfer_msg(i2c_dev, &msgs[i], NULL);
if (ret)
break;
}
--
2.8.2
next prev parent reply other threads:[~2016-09-19 15:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-19 15:26 [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes Noralf Trønnes
2016-09-19 15:26 ` Noralf Trønnes [this message]
2016-09-20 7:19 ` [PATCH 2/3] i2c: bcm2835: Add support for combined write-read transfer Martin Sperl
2016-09-20 8:41 ` Noralf Trønnes
2016-09-20 10:15 ` Martin Sperl
2016-09-20 10:56 ` Noralf Trønnes
2016-09-20 11:29 ` kernel
2016-09-21 13:45 ` Noralf Trønnes
2016-09-19 15:26 ` [PATCH 3/3] i2c: bcm2835: Use ratelimited logging on transfer errors Noralf Trønnes
2016-09-19 16:51 ` [PATCH 1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes Eric Anholt
2016-09-19 17:36 ` Noralf Trønnes
2016-09-20 6:46 ` Martin Sperl
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