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Message-ID: <c9b234e2-983f-4d24-a379-5d61ae9408cc@linux.ibm.com>
Date: Wed, 17 Apr 2024 08:50:15 -0500
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Subject: Re: [PATCH v2 25/31] i2c: fsi: Calculate clock divider from local bus
 frequency
To: Guenter Roeck <linux@roeck-us.net>
Cc: Andi Shyti <andi.shyti@kernel.org>, devicetree@vger.kernel.org,
        conor+dt@kernel.org, alistair@popple.id.au,
        linux-kernel@vger.kernel.org, lakshmiy@us.ibmcom,
        linux-i2c@vger.kernel.org, krzysztof.kozlowski+dt@linaro.org,
        linux-fsi@lists.ozlabs.org, robh@kernel.org
References: <20240226165321.91976-1-eajames@linux.ibm.com>
 <20240226165321.91976-26-eajames@linux.ibm.com>
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 <6e34260b-7d8e-4c86-9a11-6727f0c83a70@roeck-us.net>
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From: Eddie James <eajames@linux.ibm.com>
In-Reply-To: <6e34260b-7d8e-4c86-9a11-6727f0c83a70@roeck-us.net>
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On 4/16/24 16:20, Guenter Roeck wrote:
> On Tue, Apr 16, 2024 at 01:09:04PM -0500, Eddie James wrote:
>> On 4/15/24 17:11, Andi Shyti wrote:
>>> Hi Eddie,
>>>
>>>> @@ -689,6 +692,20 @@ static int fsi_i2c_probe(struct device *dev)
>>>>    	mutex_init(&i2c->lock);
>>>>    	i2c->fsi = to_fsi_dev(dev);
>>>>    	INIT_LIST_HEAD(&i2c->ports);
>>>> +	i2c->clock_div = I2C_DEFAULT_CLK_DIV;
>>>> +
>>>> +	lbus = fsi_device_local_bus_frequency(i2c->fsi);
>>>> +	if (lbus) {
>>>> +		u32 clock = I2C_DEFAULT_CLK_RATE;
>>> I don't see the need for initialization.
>>
>> Does device_property_read_u32 set clock if the property isn't found? If not,
>> it needs to be initialized here. Or I can set it in an else statement from
>> device_property_read_u32.
>>
>>
>>>> +
>>>> +		if (!device_property_read_u32(dev, "clock-frequency", &clock)) {
>>>> +			if (!clock)
>>>> +				clock = I2C_DEFAULT_CLK_RATE;
>>>> +		}
> 		if (device_property_read_u32(dev, "clock-frequency", &clock) || !clock)
> 			clock = I2C_DEFAULT_CLK_RATE;


Nice one, thanks.


>
>>>> +
>>>> +		// i2c clock rate = local bus clock / (4 * (i2c clock div + 1))
>>> You forgot to remove this.
>>
>> I actually meant to leave that comment to explain how the clock rate is
>> calculated, as the reverse calculation in the code is a little more
>> confusing.
>>
> Partially that is because you implemented DIV_ROUND_UP() manually.


Thanks Guenter, good point.


Eddie


>>> Andi
>>>
>>>> +		i2c->clock_div = (((lbus + (clock - 1)) / clock) / 4) - 1;
> 				= DIV_ROUND_UP(lbus, clock) / 4 - 1
>
> Guenter