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Rewrite iicdev_writeto() to use a single buffer and a single iic_msg, rather

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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.
This commit is contained in:
Ian Lepore 2019-11-21 19:13:05 +00:00
parent 5bebf8b402
commit e3c42ad809
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=354973
1 changed files with 37 additions and 15 deletions
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52
sys/dev/iicbus/iiconf.c
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@ -540,25 +540,47 @@ iicdev_readfrom(device_t slavedev, uint8_t regaddr, void *buffer,
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 = &regaddr;
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);
}