linux-kernel - Re: [PATCH 07/19] media: i2c: ds90ub953: Speed-up I2C watchdog timer

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Message-ID: <7e034745-831a-4518-8c4e-003fa7773a57@ideasonboard.com>
Date: Fri, 24 Jan 2025 15:19:32 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, Devarsh Thakkar <devarsht@...com>,
 Jai Luthra <jai.luthra@...asonboard.com>
Subject: Re: [PATCH 07/19] media: i2c: ds90ub953: Speed-up I2C watchdog timer

Hi,

On 15/01/2025 16:17, Sakari Ailus wrote:
> Moi,
> 
> On Fri, Jan 10, 2025 at 11:14:07AM +0200, Tomi Valkeinen wrote:
>> From: Jai Luthra <jai.luthra@...asonboard.com>
>>
>> On the I2C bus for remote clients (sensors), by default the watchdog
>> timer expires in 1s. To allow for a quicker system bring-up time, TI
>> recommends to speed it up to 50us [1].
>>
>> [1]: Section 7.3.1.1 - https://www.ti.com/lit/gpn/ds90ub953-q1
>>
>> Signed-off-by: Jai Luthra <jai.luthra@...asonboard.com>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>> ---
>>   drivers/media/i2c/ds90ub953.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/media/i2c/ds90ub953.c b/drivers/media/i2c/ds90ub953.c
>> index 99a4852b9381..6c36980e8beb 100644
>> --- a/drivers/media/i2c/ds90ub953.c
>> +++ b/drivers/media/i2c/ds90ub953.c
>> @@ -54,6 +54,10 @@
>>   #define UB953_REG_CLKOUT_CTRL0			0x06
>>   #define UB953_REG_CLKOUT_CTRL1			0x07
>>   
>> +#define UB953_REG_I2C_CONTROL2			0x0a
>> +#define UB953_REG_I2C_CONTROL2_SDA_OUTPUT_SETUP_SHIFT	4
>> +#define UB953_REG_I2C_CONTROL2_BUS_SPEEDUP	BIT(1)
>> +
>>   #define UB953_REG_SCL_HIGH_TIME			0x0b
>>   #define UB953_REG_SCL_LOW_TIME			0x0c
>>   
>> @@ -1320,6 +1324,13 @@ static int ub953_hw_init(struct ub953_data *priv)
>>   	if (ret)
>>   		return ret;
>>   
>> +	v = 0;
>> +	v |= 1 << UB953_REG_I2C_CONTROL2_SDA_OUTPUT_SETUP_SHIFT;
> 
> BIT()? Or at least 1U <<< ...;.

It's a three-bit field, the value just happens to be 1. What's wrong 
with 1 << SHIFT?

> 
>> +	v |= UB953_REG_I2C_CONTROL2_BUS_SPEEDUP;
>> +	ret = ub953_write(priv, UB953_REG_I2C_CONTROL2, v, NULL);
> 
> I'd just do this without a temporary variable. If you prefer to keep it, do
> assign the first calculated value there first and remove the assignment to
> zero.

I think we can do without.

>> +	if (ret)
>> +		return ret;
> 
> No need for this.

No, but it keeps the code structure consistent and allows easy 
future/debug modifications.

  Tomi