On Tue, Jun 2, 2009 at 5:12 PM, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote:
> 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);
> }
BTW, since you're touching these lines anyway, please clean up the
whitespace usage. Since you have to break the line anyway, it no
longer makes sense for the "ret = " to be on a separate line anymore.
g.
--
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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