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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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