Hi Esben and Ben,
Sorry for the lateness in reviewing this. FWIW, here are my comments.
g.
On Mon, May 18, 2009 at 11:22 PM, Esben Haabendal
<eha@xxxxxxxxxxxxxxxxxx> wrote:
> This fixes MAL (arbitration lost) bug caused by illegal use of
> RSTA (repeated START) after STOP condition generated after last byte
> of reads. With this patch, it is possible to do an i2c_transfer() with
> additional i2c_msg's following the I2C_M_RD messages.
>
> It still needs to be resolved if it is possible to fix this issue
> by removing the STOP condition after reads in a robust way.
>
> Signed-off-by: Esben Haabendal <eha@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/i2c/busses/i2c-mpc.c | 9 +++++++--
> 1 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c
> index 4af5c09..0199f9a 100644
> --- a/drivers/i2c/busses/i2c-mpc.c
> +++ b/drivers/i2c/busses/i2c-mpc.c
> @@ -456,17 +456,22 @@ static int mpc_xfer(struct i2c_adapter *adap, struct
> i2c_msg *msgs, int num)
> }
>
> for (i = 0; ret >= 0 && i < num; i++) {
> + int restart = i;
> pmsg = &msgs[i];
> dev_dbg(i2c->dev,
> "Doing %s %d bytes to 0x%02x - %d of %d messages\n",
> pmsg->flags & I2C_M_RD ? "read" : "write",
> pmsg->len, pmsg->addr, i + 1, num);
> + if (i > 0 && ((pmsg - 1)->flags & I2C_M_RD))
> + restart = 0;
> if (pmsg->flags & I2C_M_RD)
> ret =
> - mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len,
> i);
> + mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len,
> + restart);
> else
> ret =
> - mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len,
> i);
> + mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len,
> + restart);
> }
Hmmm, seems to be a rather convoluted code path. Surely this could be
handled in a clearer way. The whole (pmsg - 1) bit raises my eyebrows
(I'd rather see msgs[i-1]). At the very least this deserves an
comment describing what it is doing. The following might be better
for the next person who has to read this code:
+ int restart = 0;
for (i = 0; ret >= 0 && i < num; i++) {
pmsg = &msgs[i];
dev_dbg(i2c->dev,
"Doing %s %d bytes to 0x%02x - %d of %d messages\n",
pmsg->flags & I2C_M_RD ? "read" : "write",
pmsg->len, pmsg->addr, i + 1, num);
if (pmsg->flags & I2C_M_RD)
ret =
- mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len,
i);
+ mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len,
+ restart);
else
ret =
- mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len,
i);
+ mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len,
+ restart);
+ /* Only set the restart flag if this was not an
I2C_M_RD transaction
+ * because it causes an illegal use of
+ * RSTA (repeated START) after STOP condition
generated after last byte
+ * of reads */
+ restart = (pmsg->flags & I2C_M_RD == 0);
}
g.
--
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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