Re: [PATCH v8 2/5] i2c: Add STM32F4 I2C driver

[Uwe Kleine-König]

Hello Cedric,

On Wed, Jan 11, 2017 at 03:20:41PM +0100, M'boumba Cedric Madianga wrote:
> >
> >> +              */
> >> +             reg = i2c_dev->base + STM32F4_I2C_CR1;
> >> +             stm32f4_i2c_clr_bits(reg, STM32F4_I2C_CR1_ACK);
> >> +             stm32f4_i2c_set_bits(reg, STM32F4_I2C_CR1_POS);
> >
> > You could get rid of this, when caching the value of CR1. Would save two
> > register reads here. This doesn't work for all registers, but it should
> > be possible to apply for most of them, maybe enough to get rid of the
> > clr_bits and set_bits function.
> 
> I agree at many places I could save registers read by not using
> clr_bits and set_bits function when the registers in question has been
> already read.
> But it is not enough to get rid of the clr_bits and set_bits function.
> For example when calling stm32f4_i2c_terminate_xfer(), the CR1
> register is never read before so set_bits function is useful.

I didn't double check the manual, but I would expect that CR1 isn't
modified by hardware. So you can cache the result in the driver data
structure and do the necessary modifications with that one.

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |