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Date:   Thu, 6 Jun 2019 16:18:44 +0200
From:   Boris Brezillon <boris.brezillon@collabora.com>
To:     Vitor Soares <Vitor.Soares@synopsys.com>
Cc:     linux-i3c@lists.infradead.org, Joao.Pinto@synopsys.com,
        Boris Brezillon <bbrezillon@kernel.org>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v2 1/3] i3c: fix i2c and i3c scl rate by bus mode
Message-ID: <20190606161844.4a6b759c@collabora.com>
In-Reply-To: <47de89f2335930df0ed6903be9afe6de4f46e503.1559821228.git.vitor.soares@synopsys.com>
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        <47de89f2335930df0ed6903be9afe6de4f46e503.1559821228.git.vitor.soares@synopsys.com>
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On Thu,  6 Jun 2019 16:00:01 +0200
Vitor Soares <Vitor.Soares@synopsys.com> wrote:

> 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.
> 
> The core was also not accounting for I3C speed limitations when
> operating in mixed slow mode and was erroneously using FM+ speed as the
> max I2C speed when operating in mixed fast mode.
> 
> Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure")
> Signed-off-by: Vitor Soares <vitor.soares@synopsys.com>
> Cc: Boris Brezillon <bbrezillon@kernel.org>
> Cc: <stable@vger.kernel.org>
> Cc: <linux-kernel@vger.kernel.org>
> ---
> Changes in v2:
>   Enhance commit message
>   Add dev_warn() in case user-defined i2c rate doesn't match LVR constraint
>   Add dev_warn() in case user-defined i3c rate lower than i2c rate.
> 
>  drivers/i3c/master.c | 61 +++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 48 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index 5f4bd52..8cd5824 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -91,6 +91,12 @@ void i3c_bus_normaluse_unlock(struct i3c_bus *bus)
>  	up_read(&bus->lock);
>  }
>  
> +static struct i3c_master_controller *
> +i3c_bus_to_i3c_master(struct i3c_bus *i3cbus)
> +{
> +	return container_of(i3cbus, struct i3c_master_controller, bus);
> +}
> +
>  static struct i3c_master_controller *dev_to_i3cmaster(struct device *dev)
>  {
>  	return container_of(dev, struct i3c_master_controller, dev);
> @@ -565,20 +571,48 @@ 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 max_i2c_scl_rate)
>  {
> -	i3cbus->mode = mode;
>  
> -	if (!i3cbus->scl_rate.i3c)
> -		i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> +	struct i3c_master_controller *master = i3c_bus_to_i3c_master(i3cbus);
>  
> -	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;
> +	i3cbus->mode = mode;
> +
> +	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 = max_i2c_scl_rate;
> +		break;
> +	case I3C_BUS_MODE_MIXED_SLOW:
> +		if (!i3cbus->scl_rate.i2c)
> +			i3cbus->scl_rate.i2c = max_i2c_scl_rate;
> +		if (!i3cbus->scl_rate.i3c ||
> +		    i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
> +			i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;
> +		break;
> +	default:
> +		return -EINVAL;
>  	}
>  
> +	if (i3cbus->scl_rate.i3c < i3cbus->scl_rate.i2c)
> +		dev_warn(&master->dev,
> +			 "i3c-scl-hz=%ld lower than i2c-scl-hz=%ld\n",
> +			 i3cbus->scl_rate.i3c, i3cbus->scl_rate.i2c);
> +
> +	if (i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_SCL_RATE &&
> +	    i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_PLUS_SCL_RATE &&
> +	    i3cbus->mode != I3C_BUS_MODE_PURE)

If you are so strict, there's clearly no point exposing an i2c-scl-hz
property. I'm still not convinced having an i2c rate that's slower than
what the I2C/I3C spec defines as the *typical* rate is a bad thing, just
like I'm not convinced having an I3C rate that's slower than the I2C
one is a problem (it's definitely a weird situation, but there's nothing
preventing that in the spec).

> +		dev_warn(&master->dev,
> +			 "i2c-scl-hz=%ld not defined according MIPI I3C spec\n"
> +			 , i3cbus->scl_rate.i2c);

The comma should be on the previous line.

> +
>  	/*
>  	 * I3C/I2C frequency may have been overridden, check that user-provided
>  	 * values are not exceeding max possible frequency.
> @@ -1966,9 +2000,6 @@ 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);
>  
> @@ -2417,6 +2448,7 @@ 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;
> @@ -2466,9 +2498,12 @@ 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;
>