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

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Message-ID: <Z6CLAtL160DEtPfz@kekkonen.localdomain>
Date: Mon, 3 Feb 2025 09:23:14 +0000
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.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

Moi,

On Fri, Jan 24, 2025 at 03:19:32PM +0200, Tomi Valkeinen wrote:
> 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?

Shifting a signed value leads to the sign bit being undefined on some
architectures.

> 
> > 
> > > +	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.

Please still remove such redundancies.

-- 
Terveisin,

Sakari Ailus