lkml.org 
[lkml]   [2017]   [Jan]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v8 2/5] i2c: Add STM32F4 I2C driver
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

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

\
 
 \ /
  Last update: 2017-01-11 16:43    [W:0.441 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site