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    SubjectRe: [PATCH 5/30] W1: feature, enable hardware strong pullup
    On Mon, 28 Jul 2008 21:14:51 -0500
    David Fries <david@fries.net> wrote:

    > Add a strong pullup option to the w1 system. This supplies extra
    > power for parasite powered devices. There is a w1_master_pullup sysfs
    > entry and enable_pullup module parameter to enable or disable the
    > strong pullup.
    >
    > The one wire bus requires at a minimum one wire and ground. The
    > common wire is used for sending and receiving data as well as
    > supplying power to devices that are parasite powered of which
    > temperature sensors can be one example. The bus must be idle and left
    > high while a temperature conversion is in progress, in addition the
    > normal pullup resister on larger networks or even higher temperatures
    > might not supply enough power. The pullup resister can't provide too
    > much pullup current, because devices need to pull the bus down to
    > write a value. This enables the strong pullup for supported hardware,
    > which can supply more current when requested. Unsupported hardware
    > will just delay with the bus high.
    >
    > The hardware USB 2490 one wire bus master has a bit on some commands
    > which will enable the strong pullup as soon as the command finishes
    > executing. To use strong pullup, call the new w1_next_pullup function
    > to register the duration. The next write command will call set_pullup
    > before sending the data, and reset the duration to zero once it
    > returns.
    >
    > Signed-off-by: David Fries <david@fries.net>
    > Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
    > ---
    > drivers/w1/w1.c | 30 ++++++++++++++++++++++
    > drivers/w1/w1.h | 12 +++++++++
    > drivers/w1/w1_int.c | 16 ++++++++++++
    > drivers/w1/w1_io.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++---
    > 4 files changed, 122 insertions(+), 4 deletions(-)
    >
    > diff --git a/drivers/w1/w1.c b/drivers/w1/w1.c
    > index 9b5c117..76274ae 100644
    > --- a/drivers/w1/w1.c
    > +++ b/drivers/w1/w1.c
    > @@ -270,6 +270,34 @@ static ssize_t w1_master_attribute_show_search(struct device *dev,
    > return count;
    > }
    >
    > +static ssize_t w1_master_attribute_store_pullup(struct device *dev,
    > + struct device_attribute *attr,
    > + const char *buf, size_t count)
    > +{
    > + struct w1_master *md = dev_to_w1_master(dev);
    > +
    > + mutex_lock(&md->mutex);
    > + md->enable_pullup = simple_strtol(buf, NULL, 0);
    > + mutex_unlock(&md->mutex);
    > + wake_up_process(md->thread);
    > +
    > + return count;
    > +}

    checkpatch says:

    WARNING: consider using strict_strtol in preference to simple_strtol
    #49: FILE: drivers/w1/w1.c:280:
    + md->enable_pullup = simple_strtol(buf, NULL, 0);

    for good reasons. The code which you have implemented will treat the
    value "45foo" as 45, which is sloppy. strict_strtoul() (if
    handled appropriately) will perform the necessary checking.

    A simple_strtol->strict_strtol conversion is a non-backward-compatible
    userspace interface change (albeit a pretty non-risky one) and should
    be done with caution.

    Please use checkpatch.


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