linux-kernel - Re: [PATCH v10 6/7] i3c: master: sysfs key for acquire bus

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Date:   Wed, 9 Jun 2021 01:33:26 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Parshuram Thombare <pthombar@...ence.com>
Cc:     slongerbeam@...il.com, vitor.soares@...opsys.com,
        linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mparab@...ence.com, praneeth@...com
Subject: Re: [PATCH v10 6/7] i3c: master: sysfs key for acquire bus

On 30/11/2020 07:20:02+0100, Parshuram Thombare wrote:
> Added support to acquire I3C bus through sysfs interface.
> 
> Signed-off-by: Parshuram Thombare <pthombar@...ence.com>
> ---
>  drivers/i3c/master.c |   18 ++++++++++++++++++
>  1 files changed, 18 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index c01ba00..beb7495 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -581,6 +581,23 @@ static ssize_t i2c_scl_frequency_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RO(i2c_scl_frequency);
>  
> +static ssize_t i3c_acquire_bus_store(struct device *dev,
> +				     struct device_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	struct i3c_master_controller *master = dev_to_i3cmaster(dev);
> +	int ret;
> +
> +	i3c_bus_normaluse_lock(&master->bus);
> +	ret = i3c_master_acquire_bus(master);
> +	i3c_bus_normaluse_unlock(&master->bus);
> +	if (!ret)
> +		i3c_master_enable_mr_events(master);
> +
> +	return ret ?: count;
> +}
> +static DEVICE_ATTR_WO(i3c_acquire_bus);
> +

I'm wondering whether we should allow userspace to actually control
that. Shouldn't we simply request mastership when a driver needs to talk
to a device on the bus? Is it really useful to have that until there is
an i3c-dev userspace interface?

>  static struct attribute *i3c_masterdev_attrs[] = {
>  	&dev_attr_mode.attr,
>  	&dev_attr_current_master.attr,
> @@ -591,6 +608,7 @@ static ssize_t i2c_scl_frequency_show(struct device *dev,
>  	&dev_attr_pid.attr,
>  	&dev_attr_dynamic_address.attr,
>  	&dev_attr_hdrcap.attr,
> +	&dev_attr_i3c_acquire_bus.attr,
>  	NULL,
>  };
>  ATTRIBUTE_GROUPS(i3c_masterdev);
> -- 
> 1.7.1
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com