Author: ian
Date: Thu Nov 21 19:13:05 2019
New Revision: 354973
URL: https://svnweb.freebsd.org/changeset/base/354973
Log:
Rewrite iicdev_writeto() to use a single buffer and a single iic_msg, rather
than effectively doing scatter/gather IO with a pair of iic_msgs that direct
the controller to do a single transfer with no bus STOP/START between the
two buffers. It turns out we have multiple i2c hardware drivers that don't
honor the NOSTOP and NOSTART flags; sometimes they just try to do the
transfers anyway, creating confusing failures or leading to corrupted data.
Modified:
head/sys/dev/iicbus/iiconf.c
Modified: head/sys/dev/iicbus/iiconf.c
==============================================================================
--- head/sys/dev/iicbus/iiconf.c Thu Nov 21 18:49:54 2019
(r354972)
+++ head/sys/dev/iicbus/iiconf.c Thu Nov 21 19:13:05 2019
(r354973)
@@ -540,25 +540,47 @@ iicdev_readfrom(device_t slavedev, uint8_t regaddr, vo
int iicdev_writeto(device_t slavedev, uint8_t regaddr, void *buffer,
uint16_t buflen, int waithow)
{
- struct iic_msg msgs[2];
- uint8_t slaveaddr;
+ struct iic_msg msg;
+ uint8_t local_buffer[32];
+ uint8_t *bufptr;
+ size_t bufsize;
+ int error;
/*
- * Two transfers back to back with no stop or start between them; first
- * we write the address then we write the data to that address, all in a
- * single transfer from two scattered buffers.
+ * Ideally, we would do two transfers back to back with no stop or start
+ * between them using an array of 2 iic_msgs; first we'd write the
+ * address byte using the IIC_M_NOSTOP flag, then we write the data
+ * using IIC_M_NOSTART, all in a single transfer. Unfortunately,
+ * several i2c hardware drivers don't support that (perhaps because the
+ * hardware itself can't support it). So instead we gather the
+ * scattered bytes into a single buffer here before writing them using a
+ * single iic_msg. This function is typically used to write a few bytes
+ * at a time, so we try to use a small local buffer on the stack, but
+ * fall back to allocating a temporary buffer when necessary.
*/
- slaveaddr = iicbus_get_addr(slavedev);
- msgs[0].slave = slaveaddr;
- msgs[0].flags = IIC_M_WR | IIC_M_NOSTOP;
- msgs[0].len = 1;
- msgs[0].buf = ®addr;
+ bufsize = buflen + 1;
+ if (bufsize <= sizeof(local_buffer)) {
+ bufptr = local_buffer;
+ } else {
+ bufptr = malloc(bufsize, M_DEVBUF,
+ (waithow & IIC_WAIT) ? M_WAITOK : M_NOWAIT);
+ if (bufptr == NULL)
+ return (errno2iic(ENOMEM));
+ }
- msgs[1].slave = slaveaddr;
- msgs[1].flags = IIC_M_WR | IIC_M_NOSTART;
- msgs[1].len = buflen;
- msgs[1].buf = buffer;
+ bufptr[0] = regaddr;
+ memcpy(&bufptr[1], buffer, buflen);
- return (iicbus_transfer_excl(slavedev, msgs, nitems(msgs), waithow));
+ msg.slave = iicbus_get_addr(slavedev);
+ msg.flags = IIC_M_WR;
+ msg.len = bufsize;
+ msg.buf = bufptr;
+
+ error = iicbus_transfer_excl(slavedev, &msg, 1, waithow);
+
+ if (bufptr != local_buffer)
+ free(bufptr, M_DEVBUF);
+
+ return (error);
}
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