diff mbox

[2/3] i2c: xlr: fix extra read/write at end of rx transfer

Message ID 1446429818-24155-2-git-send-email-mans@mansr.com
State Changes Requested
Headers show

Commit Message

Måns Rullgård Nov. 2, 2015, 2:03 a.m. UTC 
The BYTECNT register holds the transfer size minus one.  Setting it
to the correct value requires a dummy read/write only for zero-length
transfers as it is impossible to request one from the hardware.  If a
zero-length transfer is requested, changing the length to 1 and setting
"buf" to a dummy location allows making the main loops less convoluted.

In other words, this patch makes the driver transfer the number of bytes
requested unless this is zero, which is not supported by the hardware,
in which case one byte is transferred instead.

Signed-off-by: Mans Rullgard <mans@mansr.com>
---
 drivers/i2c/busses/i2c-xlr.c | 51 +++++++++++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 20 deletions(-)

Comments

Wolfram Sang Dec. 15, 2015, 12:21 p.m. UTC | #1 
On Mon, Nov 02, 2015 at 02:03:37AM +0000, Mans Rullgard wrote:
> The BYTECNT register holds the transfer size minus one.  Setting it
> to the correct value requires a dummy read/write only for zero-length
> transfers as it is impossible to request one from the hardware.  If a
> zero-length transfer is requested, changing the length to 1 and setting
> "buf" to a dummy location allows making the main loops less convoluted.
> 
> In other words, this patch makes the driver transfer the number of bytes
> requested unless this is zero, which is not supported by the hardware,
> in which case one byte is transferred instead.

Uh, this is wrong, zero byte should really not transfer anything. We
need to fix that and bail out, so probably something like

	if (!len)
		return -EOPNOTSUPP;

Also, the xlr_func() should mask out I2C_FUNC_SMBUS_QUICK.

Other than that, the patch looks good to me.

Out of curiosity, your first driver had the registers 32bit apart. Now
you can deal with 8bit. Is this configurable on this SoC?

Thanks,

   Wolfram
Måns Rullgård Dec. 15, 2015, 12:48 p.m. UTC | #2 
Wolfram Sang <wsa@the-dreams.de> writes:

> On Mon, Nov 02, 2015 at 02:03:37AM +0000, Mans Rullgard wrote:
>> The BYTECNT register holds the transfer size minus one.  Setting it
>> to the correct value requires a dummy read/write only for zero-length
>> transfers as it is impossible to request one from the hardware.  If a
>> zero-length transfer is requested, changing the length to 1 and setting
>> "buf" to a dummy location allows making the main loops less convoluted.
>> 
>> In other words, this patch makes the driver transfer the number of bytes
>> requested unless this is zero, which is not supported by the hardware,
>> in which case one byte is transferred instead.
>
> Uh, this is wrong, zero byte should really not transfer anything. We
> need to fix that and bail out, so probably something like
>
> 	if (!len)
> 		return -EOPNOTSUPP;

So the existing driver is wrong to allow it.  Makes sense to drop that.

> Also, the xlr_func() should mask out I2C_FUNC_SMBUS_QUICK.

OK.

> Other than that, the patch looks good to me.
>
> Out of curiosity, your first driver had the registers 32bit apart. Now
> you can deal with 8bit. Is this configurable on this SoC?

It's all 32 bits.  The XLR driver uses a u32 * to access the registers.
diff mbox

Patch

diff --git a/drivers/i2c/busses/i2c-xlr.c b/drivers/i2c/busses/i2c-xlr.c
index 10fb916..c1afc3e 100644
--- a/drivers/i2c/busses/i2c-xlr.c
+++ b/drivers/i2c/busses/i2c-xlr.c
@@ -90,37 +90,45 @@  static int xlr_i2c_tx(struct xlr_i2c_private *priv,  u16 len,
 	u32 i2c_status;
 	int pos, timedout;
 	u8 offset, byte;
+	u32 xfer;
+
+	if (!len) {
+		byte = 0;
+		buf = &byte;
+		len = 1;
+	}
 
 	offset = buf[0];
 	xlr_i2c_wreg(priv->iobase, XLR_I2C_ADDR, offset);
 	xlr_i2c_wreg(priv->iobase, XLR_I2C_DEVADDR, addr);
 	xlr_i2c_wreg(priv->iobase, XLR_I2C_CFG,
 			XLR_I2C_CFG_ADDR | priv->cfg->cfg_extra);
-	xlr_i2c_wreg(priv->iobase, XLR_I2C_BYTECNT, len - 1);
 
 	timeout = msecs_to_jiffies(XLR_I2C_TIMEOUT);
 	stoptime = jiffies + timeout;
 	timedout = 0;
-	pos = 1;
-retry:
+
 	if (len == 1) {
-		xlr_i2c_wreg(priv->iobase, XLR_I2C_STARTXFR,
-				XLR_I2C_STARTXFR_ND);
+		xlr_i2c_wreg(priv->iobase, XLR_I2C_BYTECNT, len - 1);
+		xfer = XLR_I2C_STARTXFR_ND;
+		pos = 1;
 	} else {
-		xlr_i2c_wreg(priv->iobase, XLR_I2C_DATAOUT, buf[pos]);
-		xlr_i2c_wreg(priv->iobase, XLR_I2C_STARTXFR,
-				XLR_I2C_STARTXFR_WR);
+		xlr_i2c_wreg(priv->iobase, XLR_I2C_BYTECNT, len - 2);
+		xlr_i2c_wreg(priv->iobase, XLR_I2C_DATAOUT, buf[1]);
+		xfer = XLR_I2C_STARTXFR_WR;
+		pos = 2;
 	}
 
+retry:
+	/* retry can only happen on the first byte */
+	xlr_i2c_wreg(priv->iobase, XLR_I2C_STARTXFR, xfer);
+
 	while (!timedout) {
 		checktime = jiffies;
 		i2c_status = xlr_i2c_rdreg(priv->iobase, XLR_I2C_STATUS);
 
-		if (i2c_status & XLR_I2C_SDOEMPTY) {
-			pos++;
-			/* need to do a empty dataout after the last byte */
-			byte = (pos < len) ? buf[pos] : 0;
-			xlr_i2c_wreg(priv->iobase, XLR_I2C_DATAOUT, byte);
+		if ((i2c_status & XLR_I2C_SDOEMPTY) && pos < len) {
+			xlr_i2c_wreg(priv->iobase, XLR_I2C_DATAOUT, buf[pos++]);
 
 			/* reset timeout on successful xmit */
 			stoptime = jiffies + timeout;
@@ -151,9 +159,15 @@  static int xlr_i2c_rx(struct xlr_i2c_private *priv, u16 len, u8 *buf, u16 addr)
 	int nbytes, timedout;
 	u8 byte;
 
+	if (!len) {
+		byte = 0;
+		buf = &byte;
+		len = 1;
+	}
+
 	xlr_i2c_wreg(priv->iobase, XLR_I2C_CFG,
 			XLR_I2C_CFG_NOADDR | priv->cfg->cfg_extra);
-	xlr_i2c_wreg(priv->iobase, XLR_I2C_BYTECNT, len);
+	xlr_i2c_wreg(priv->iobase, XLR_I2C_BYTECNT, len - 1);
 	xlr_i2c_wreg(priv->iobase, XLR_I2C_DEVADDR, addr);
 
 	timeout = msecs_to_jiffies(XLR_I2C_TIMEOUT);
@@ -167,14 +181,11 @@  retry:
 		checktime = jiffies;
 		i2c_status = xlr_i2c_rdreg(priv->iobase, XLR_I2C_STATUS);
 		if (i2c_status & XLR_I2C_RXRDY) {
-			if (nbytes > len)
+			if (nbytes >= len)
 				return -EIO;	/* should not happen */
 
-			/* we need to do a dummy datain when nbytes == len */
-			byte = xlr_i2c_rdreg(priv->iobase, XLR_I2C_DATAIN);
-			if (nbytes < len)
-				buf[nbytes] = byte;
-			nbytes++;
+			buf[nbytes++] =
+				xlr_i2c_rdreg(priv->iobase, XLR_I2C_DATAIN);
 
 			/* reset timeout on successful read */
 			stoptime = jiffies + timeout;