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SubjectRe: [PATCH] i2c/busses: (mpc) Add support for SMBUS_READ_BLOCK_DATA
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Hi Jean,

On Tue, 2011-11-15 at 03:54 -0500, Jean Delvare wrote:
> Hi Guenter,
>
> On Mon, 14 Nov 2011 22:27:42 -0800, Guenter Roeck wrote:
> > Add support for SMBUS_READ_BLOCK_DATA to the i2c-mpc bus driver.
> > Required to support the PMBus zl6100 driver with i2c-mpc.
> >
> > Reported-by: Tang Yuantian <B29983@freescale.com>
> > Cc: Tang Yuantian <B29983@freescale.com>
> > Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
> > ---
> > drivers/i2c/busses/i2c-mpc.c | 33 +++++++++++++++++++++++++--------
> > 1 files changed, 25 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c
> > index 107397a..77aade7 100644
> > --- a/drivers/i2c/busses/i2c-mpc.c
> > +++ b/drivers/i2c/busses/i2c-mpc.c
> > @@ -454,7 +454,7 @@ static int mpc_write(struct mpc_i2c *i2c, int target,
> > }
> >
> > static int mpc_read(struct mpc_i2c *i2c, int target,
> > - u8 *data, int length, int restart)
> > + u8 *data, int length, int restart, bool block)
>
> bool block would be better named bool recv_len IMHO. It will be set to
> 0 for I2C block reads, which is confusing.
>
Ok.

> > {
> > unsigned timeout = i2c->adap.timeout;
> > int i, result;
> > @@ -470,7 +470,7 @@ static int mpc_read(struct mpc_i2c *i2c, int target,
> > return result;
> >
> > if (length) {
> > - if (length == 1)
> > + if (length == 1 && !block)
> > writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_TXAK);
> > else
> > writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA);
> > @@ -479,17 +479,28 @@ static int mpc_read(struct mpc_i2c *i2c, int target,
> > }
> >
> > for (i = 0; i < length; i++) {
> > + u8 byte;
> > +
> > result = i2c_wait(i2c, timeout, 0);
> > if (result < 0)
> > return result;
> >
> > + byte = readb(i2c->base + MPC_I2C_DR);
> > + /*
> > + * Adjust length if first received byte is length
> > + */
> > + if (i == 0 && block) {
> > + if (byte == 0 || byte > I2C_SMBUS_BLOCK_MAX)
> > + return -EPROTO;
> > + length += byte;
> > + }
> > + data[i] = byte;
> > /* Generate txack on next to last byte */
> > if (i == length - 2)
> > writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_TXAK);
> > /* Do not generate stop on last byte */
> > if (i == length - 1)
> > writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_MTX);
> > - data[i] = readb(i2c->base + MPC_I2C_DR);
> > }
>
> This needs careful testing (which I can't do.) There may have been a
> reason why the read was done after the writes. Swapping the commands
> may be the wrong thing to do. The dummy read earlier in this function
> suggests that maybe changes to CCR do not take effect until you read
> from (or write to) the DR register.
>
Interestingly there is not always a read after a write to ccr. If a read
is necessary, I'd rather add a dummy read after writeccr().

> Can't the above be rewritten to keep the order of the commands as it
> was before? AFAICS it would only take one or two extra tests.
>
The resulting code would not support 1-byte block reads. That seems to
be unnecessary and undesirable.

> Note that the hardware implementation may make it difficult or even
> impossible to properly support SMBus block reads of 1 byte. Not sure
> what should be done when this can be supported and still happens...
> Returning -EOPNOTSUPP I guess, and then probably the I2C engine needs
> some form of reset.
>
The code generates stop after returning from mpc_read(). That should
hopefully take care of error conditions. I could add
writeccr(i2c, 0);
into the error path, as is done for timeouts, but I am not sure if that
would be helpful or not.

Either case, I'd like to avoid that case. I think it would be better to
get some test coverage from someone who has access to a board, or even
better feedback from someone who knows the chip.

Yuantian indicated that my raw patch worked with the zl6100 driver, and
the PMBus driver does a lot of accesses, so we do have some test
coverage already.

> >
> > return length;
> > @@ -532,12 +543,17 @@ static int mpc_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
> > "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);
> > - else
> > + if (pmsg->flags & I2C_M_RD) {
> > + bool block = pmsg->flags & I2C_M_RECV_LEN;
>
> Here again I'd rather name it bool recv_len for clarity.
>
Ok.

> > +
> > + ret = mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len, i,
> > + block);
>
> That's a lot of parameters, most coming from pmsg. It would be more
> efficient to pass pmsg itself. Not directly related to your patch,
> admittedly, but it makes the problem more obvious. Maybe a cleanup for
> later.
>
later ...

> > + if (block && ret > 0)
> > + pmsg->len = ret;
> > + } else {
> > ret =
> > mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len, i);
> > + }
> > }
> > mpc_i2c_stop(i2c);
> > return (ret < 0) ? ret : num;
> > @@ -545,7 +561,8 @@ static int mpc_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
> >
> > static u32 mpc_functionality(struct i2c_adapter *adap)
> > {
> > - return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
> > + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL
> > + | I2C_FUNC_SMBUS_READ_BLOCK_DATA;
>
> You could add I2C_FUNC_SMBUS_BLOCK_PROC_CALL too, even though I
> don't know of any slave driver using it.
>
Sure.

> > }
> >
> > static const struct i2c_algorithm mpc_algo = {
>
>
Thanks,
Guenter




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