linux-kernel - Re: [RESEND PATCH 1/2] i2c: enable buses to save their clock frequency in adapter

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Date:   Mon, 29 Oct 2018 15:49:18 +0100
From:   Ludovic Desroches <ludovic.desroches@...rochip.com>
To:     Tudor Ambarus - M18064 <Tudor.Ambarus@...rochip.com>
CC:     "wsa@...-dreams.de" <wsa@...-dreams.de>,
        Nicolas Ferre - M43238 <Nicolas.Ferre@...rochip.com>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH 1/2] i2c: enable buses to save their clock
 frequency in adapter

On Tue, Oct 23, 2018 at 11:20:39AM +0200, Tudor Ambarus - M18064 wrote:
> The clock-frequency property is not mandatory for the i2c buses. If it's
> not present in the device tree, the buses __usually__ assume it's 100kHZ
> (see altera, at91, axxia, etc.). Broadcom uses a 375kHZ default
> clock-frequency, so the default clock frequency varies from bus to bus.
> 
> There are i2c clients that need to know the bus clock frequency in order to
> compute their wake token (see atecc508a i2c client).
> 
> The clock-frequency value has to be propagated to the i2c clients, otherwise,
> if they will not find the i2c bus clock frequency in the device tree, they
> will have to make their own assumption of the clock frequency.
> 
> Spare the i2c clients of making wrong assumptions of the i2c bus clock
> frequency and enable the buses to save their clock frequency in adapter.
> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
Reviwed-by: Ludovic Desroches <ludovic.desroches@...rochip.com>

> ---
>  include/linux/i2c.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 65b4eaed1d96..f238da204c49 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -677,6 +677,7 @@ struct i2c_adapter {
>  	struct rt_mutex bus_lock;
>  	struct rt_mutex mux_lock;
>  
> +	u32 bus_freq_hz;
>  	int timeout;			/* in jiffies */
>  	int retries;
>  	struct device dev;		/* the adapter device */
> -- 
> 2.9.4
>