linux-kernel - Re: [PATCH 2/3] i3c: add mixed limited bus mode

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Message-ID: <20190416080049.5a6053b0@collabora.com>
Date:   Tue, 16 Apr 2019 08:00:49 +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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] i3c: add mixed limited bus mode

Hi Vitor,

On Mon, 15 Apr 2019 20:46:42 +0200
Vitor Soares <vitor.soares@...opsys.com> wrote:

> The i3c bus spec define a bus configuration where the i2c devices

		   ^defines			    I2C devices...

> doesn't have the 50ns filter yet they allow the SDR max speed.

  ^don't	^ a 50ns filter but support SCL running at SDR max
rate (12MHz).

> 
> This patch introduce the limited bus mode so the users can use

	     ^introduces		    ^ so that users

> a higher speed on presence of i2c devices index 1.

		 ^in

> 
> Signed-off-by: Vitor Soares <vitor.soares@...opsys.com>
> Cc: Boris Brezillon <bbrezillon@...nel.org>
> Cc: <linux-kernel@...r.kernel.org>
> ---
>  drivers/i3c/master.c       | 5 +++++
>  include/linux/i3c/master.h | 5 +++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index 1c4a86a..46d3774 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -463,6 +463,7 @@ static int i3c_bus_init(struct i3c_bus *i3cbus)
>  static const char * const i3c_bus_mode_strings[] = {
>  	[I3C_BUS_MODE_PURE] = "pure",
>  	[I3C_BUS_MODE_MIXED_FAST] = "mixed-fast",
> +	[I3C_BUS_MODE_MIXED_LIMITED] = "mixed-limited",
>  	[I3C_BUS_MODE_MIXED_SLOW] = "mixed-slow",
>  };
>  
> @@ -575,6 +576,7 @@ int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode,
>  			i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
>  		break;
>  	case I3C_BUS_MODE_MIXED_FAST:
> +	case I3C_BUS_MODE_MIXED_LIMITED:
>  		if (!i3cbus->scl_rate.i3c)
>  			i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
>  		if (!i3cbus->scl_rate.i2c)
> @@ -2481,6 +2483,9 @@ int i3c_master_register(struct i3c_master_controller *master,
>  				mode = I3C_BUS_MODE_MIXED_FAST;
>  			break;
>  		case I3C_LVR_I2C_INDEX(1):
> +			if (mode < I3C_BUS_MODE_MIXED_LIMITED)
> +				mode = I3C_BUS_MODE_MIXED_LIMITED;
> +			break;
>  		case I3C_LVR_I2C_INDEX(2):
>  			if (mode < I3C_BUS_MODE_MIXED_SLOW)
>  				mode = I3C_BUS_MODE_MIXED_SLOW;
> diff --git a/include/linux/i3c/master.h b/include/linux/i3c/master.h
> index 44fb3cf..740235e 100644
> --- a/include/linux/i3c/master.h
> +++ b/include/linux/i3c/master.h
> @@ -250,12 +250,17 @@ struct i3c_device {
>   *			     the bus. The only impact in this mode is that the
>   *			     high SCL pulse has to stay below 50ns to trick I2C
>   *			     devices when transmitting I3C frames
> + * @I3C_BUS_MODE_MIXED_LIMITED: I2C devices without 50ns spike filter are
> + *				present on the bus. However they allows
> + *				compliance up to the maximum SDR SCL clock
> + *				frequency.

						    However they support
				SCL clock running at maximum SDR rate
				(12.5MHz).

>   * @I3C_BUS_MODE_MIXED_SLOW: I2C devices without 50ns spike filter are present
>   *			     on the bus
>   */
>  enum i3c_bus_mode {
>  	I3C_BUS_MODE_PURE,
>  	I3C_BUS_MODE_MIXED_FAST,
> +	I3C_BUS_MODE_MIXED_LIMITED,
>  	I3C_BUS_MODE_MIXED_SLOW,
>  };
>  

The code itself looks good.

Thanks,

Boris