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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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