linux-kernel - Re: [PATCH 1/3] i3c: fix i2c and i3c scl rate by bus mode

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Message-ID: <20190416075041.22f8e849@collabora.com>
Date:   Tue, 16 Apr 2019 07:50:41 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Vitor Soares <vitor.soares@...opsys.com>
Cc:     linux-i3c@...ts.infradead.org, joao.pinto@...opsys.com,
        Boris Brezillon <bbrezillon@...nel.org>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] i3c: fix i2c and i3c scl rate by bus mode

On Mon, 15 Apr 2019 20:46:41 +0200
Vitor Soares <vitor.soares@...opsys.com> wrote:

> Currently in case of mixed slow bus topologie and all i2c devices
> support FM+ speed, the i3c subsystem limite the SCL to FM speed.

"
Currently the I3C framework limits SCL frequency to FM speed when
dealing with a mixed slow bus, even if all I2C devices are FM+ capable.
"

> Also in case on mixed slow bus mode the max speed for both
> i2c or i3c transfers is FM or FM+.

Looks like you're basically repeating what you said above.

> 
> This patch fix the definition of i2c and i3c scl rate based on bus

	     ^fixes					      on the bus

> topologie and LVR[4] if no user input.

  ^topology		^if the rate is not already specified by the user.

> In case of mixed slow mode the i3c scl rate is overridden.

							   ^ with the max
I2C rate.

> 
> Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure")
> Signed-off-by: Vitor Soares <vitor.soares@...opsys.com>
> Cc: Boris Brezillon <bbrezillon@...nel.org>
> Cc: <stable@...r.kernel.org>
> Cc: <linux-kernel@...r.kernel.org>
> ---
>  drivers/i3c/master.c | 39 +++++++++++++++++++++++++--------------
>  1 file changed, 25 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index 909c2ad..1c4a86a 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -564,20 +564,30 @@ static const struct device_type i3c_masterdev_type = {
>  	.groups	= i3c_masterdev_groups,
>  };
>  
> -int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode)
> +int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode,
> +		     unsigned long i2c_scl_rate)


Can we rename the last arg into max_i2c_scl_rate?

>  {
>  	i3cbus->mode = mode;
>  
> -	if (!i3cbus->scl_rate.i3c)
> -		i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> -
> -	if (!i3cbus->scl_rate.i2c) {
> -		if (i3cbus->mode == I3C_BUS_MODE_MIXED_SLOW)
> -			i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
> -		else
> -			i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> +	switch (i3cbus->mode) {
> +	case I3C_BUS_MODE_PURE:
> +		if (!i3cbus->scl_rate.i3c)
> +			i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> +		break;
> +	case I3C_BUS_MODE_MIXED_FAST:
> +		if (!i3cbus->scl_rate.i3c)
> +			i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> +		if (!i3cbus->scl_rate.i2c)
> +			i3cbus->scl_rate.i2c = i2c_scl_rate;
> +		break;
> +	case I3C_BUS_MODE_MIXED_SLOW:
> +		if (!i3cbus->scl_rate.i2c)
> +			i3cbus->scl_rate.i2c = i2c_scl_rate;
> +		i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;

Maybe we should do

		if (!i3cbus->scl_rate.i3c ||
		    i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
			i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;
					   
Just in case the I3C rate forced by the user is lower than the max I2C
rate.

The patch looks good otherwise.

> +		break;
> +	default:
> +		return -EINVAL;
>  	}
> -
>  	/*
>  	 * I3C/I2C frequency may have been overridden, check that user-provided
>  	 * values are not exceeding max possible frequency.
> @@ -1980,9 +1990,6 @@ of_i3c_master_add_i2c_boardinfo(struct i3c_master_controller *master,
>  	/* LVR is encoded in reg[2]. */
>  	boardinfo->lvr = reg[2];
>  
> -	if (boardinfo->lvr & I3C_LVR_I2C_FM_MODE)
> -		master->bus.scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
> -
>  	list_add_tail(&boardinfo->node, &master->boardinfo.i2c);
>  	of_node_get(node);
>  
> @@ -2432,6 +2439,7 @@ int i3c_master_register(struct i3c_master_controller *master,
>  			const struct i3c_master_controller_ops *ops,
>  			bool secondary)
>  {
> +	unsigned long i2c_scl_rate = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
>  	struct i3c_bus *i3cbus = i3c_master_get_bus(master);
>  	enum i3c_bus_mode mode = I3C_BUS_MODE_PURE;
>  	struct i2c_dev_boardinfo *i2cbi;
> @@ -2481,9 +2489,12 @@ int i3c_master_register(struct i3c_master_controller *master,
>  			ret = -EINVAL;
>  			goto err_put_dev;
>  		}
> +
> +		if (i2cbi->lvr & I3C_LVR_I2C_FM_MODE)
> +			i2c_scl_rate = I3C_BUS_I2C_FM_SCL_RATE;
>  	}
>  
> -	ret = i3c_bus_set_mode(i3cbus, mode);
> +	ret = i3c_bus_set_mode(i3cbus, mode, i2c_scl_rate);
>  	if (ret)
>  		goto err_put_dev;
>