linux-kernel - Re: [PATCH v2] i2c: npcm7xx: Support changing bus speed using debugfs.

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Message-ID: <20201013115023.GL4077@smile.fi.intel.com>
Date:   Tue, 13 Oct 2020 14:50:23 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Tali Perry <tali.perry1@...il.com>
Cc:     wsa@...nel.org, xqiu@...gle.com, kunyi@...gle.com,
        benjaminfair@...gle.com, avifishman70@...il.com, joel@....id.au,
        tmaimon77@...il.com, linux-i2c@...r.kernel.org,
        openbmc@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] i2c: npcm7xx: Support changing bus speed using
 debugfs.

On Tue, Oct 13, 2020 at 01:03:14PM +0300, Tali Perry wrote:
> Systems that can dynamically add and remove slave devices
> often need to change the bus speed in runtime.
> This patch expose the bus frequency to the user.
> This feature can also be used for test automation.

> --
> v2 -> v1:
> 	- Fix typos.
> 	- Remove casting to u64.
> 	
> v1: initial version

Above block should go after cutter '---' (see below) line...

> Fixes: 56a1485b102e (i2c: npcm7xx: Add Nuvoton NPCM I2C controller driver)
> Signed-off-by: Tali Perry <tali.perry1@...il.com>
> ---

...here.

>  drivers/i2c/busses/i2c-npcm7xx.c | 35 ++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)

As we discussed previously I'm not a fan of the functionality this gives and a
way it's done, but this is debugfs and not anyhow an ABI. Also it's localized
inside one driver. In the future we may come up with better approach.

That said, no objections from me.

> diff --git a/drivers/i2c/busses/i2c-npcm7xx.c b/drivers/i2c/busses/i2c-npcm7xx.c
> index 2ad166355ec9..633ac67153e2 100644
> --- a/drivers/i2c/busses/i2c-npcm7xx.c
> +++ b/drivers/i2c/busses/i2c-npcm7xx.c
> @@ -2208,6 +2208,40 @@ static const struct i2c_algorithm npcm_i2c_algo = {
>  /* i2c debugfs directory: used to keep health monitor of i2c devices */
>  static struct dentry *npcm_i2c_debugfs_dir;
>  
> +static int i2c_speed_get(void *data, u64 *val)
> +{
> +	struct npcm_i2c *bus = data;
> +
> +	*val = bus->bus_freq;
> +	return 0;
> +}
> +
> +static int i2c_speed_set(void *data, u64 val)
> +{
> +	struct npcm_i2c *bus = data;
> +	int ret;
> +
> +	if (val < I2C_FREQ_MIN_HZ || val > I2C_FREQ_MAX_HZ)
> +		return -EINVAL;
> +
> +	if (val == bus->bus_freq)
> +		return 0;
> +
> +	i2c_lock_bus(&bus->adap, I2C_LOCK_ROOT_ADAPTER);
> +
> +	npcm_i2c_int_enable(bus, false);
> +
> +	ret = npcm_i2c_init_module(bus, I2C_MASTER, (u32)val);
> +
> +	i2c_unlock_bus(&bus->adap, I2C_LOCK_ROOT_ADAPTER);
> +
> +	if (ret)
> +		return -EAGAIN;
> +
> +	return 0;
> +}
> +DEFINE_DEBUGFS_ATTRIBUTE(i2c_clock_ops, i2c_speed_get, i2c_speed_set, "%llu\n");
> +
>  static void npcm_i2c_init_debugfs(struct platform_device *pdev,
>  				  struct npcm_i2c *bus)
>  {
> @@ -2223,6 +2257,7 @@ static void npcm_i2c_init_debugfs(struct platform_device *pdev,
>  	debugfs_create_u64("rec_succ_cnt", 0444, d, &bus->rec_succ_cnt);
>  	debugfs_create_u64("rec_fail_cnt", 0444, d, &bus->rec_fail_cnt);
>  	debugfs_create_u64("timeout_cnt", 0444, d, &bus->timeout_cnt);
> +	debugfs_create_file("i2c_speed", 0644, d, bus, &i2c_clock_ops);
>  
>  	bus->debugfs = d;
>  }
> 
> base-commit: 865c50e1d279671728c2936cb7680eb89355eeea
> -- 
> 2.22.0
> 

-- 
With Best Regards,
Andy Shevchenko