[U-Boot] [PATCH 3/3] mxc_i2c: remove setting speed at each start

[Marek Vasut]

Dear Troy Kisky,

> On 5/5/2012 6:08 AM, Marek Vasut wrote:
> > Dear Troy Kisky,
> > 
> >> On 4/24/2012 8:33 PM, Troy Kisky wrote:
> >>> Other then being very weird, this code was also wrong.
> >>> For example, say I set speed to 100K. I'll read back the speed
> >>> as 85937. But the speed is really 85937.5, so we I reset
> >>> the speed to 85937, I'll get 73660.7. After a couple of transactions
> >>> my speed is now exactly 68750 so it will remain there.
> >>> 
> >>> Signed-off-by: Troy Kisky<troy.kisky at boundarydevices.com>
> >>> ---
> >>> 
> >>>    drivers/i2c/mxc_i2c.c |    6 ------
> >>>    1 files changed, 0 insertions(+), 6 deletions(-)
> >>> 
> >>> diff --git a/drivers/i2c/mxc_i2c.c b/drivers/i2c/mxc_i2c.c
> >>> index 416ffee..fc68062 100644
> >>> --- a/drivers/i2c/mxc_i2c.c
> >>> +++ b/drivers/i2c/mxc_i2c.c
> >>> @@ -231,12 +231,6 @@ int i2c_imx_start(void)
> >>> 
> >>>    	struct mxc_i2c_regs *i2c_regs = (struct mxc_i2c_regs *)I2C_BASE;
> >>>    	unsigned int temp = 0;
> >>>    	int result;
> >>> 
> >>> -	int speed = i2c_get_bus_speed();
> >>> -	u8 clk_idx = i2c_imx_get_clk(speed);
> >>> -	u8 idx = i2c_clk_div[clk_idx][1];
> >>> -
> >>> -	/* Store divider value */
> >>> -	writeb(idx,&i2c_regs->ifdr);
> >>> 
> >>>    	/* Enable I2C controller */
> >>>    	writeb(0,&i2c_regs->i2sr);
> >> 
> >> Marek would you care to ack/nak this? It is deleting code that you
> >> added.
> > 
> > Ok, who will set the controller speed if you remove this?
> 
> i2c_init is the only function that writes the ifdr register after this
> patch.

And i2c_init() is called on every boot. Correct?

> This is fine because this register is not affected by a software reset.

I take it you verified this or that you're sure here :)

> If this register were affected by a software reset, then the current code
> would not work either, as i2c_imx_start is reading from this register
> before trying(and often failing) to set it to the same value.

Reading from ifdr? That seems indeed wrong :-(

Well ... I have no objection then

Acked-by: Marek Vasut <marex at denx.de>

> >> Thanks
> >> Troy
> > 
> > Best regards,
> > Marek Vasut

Best regards,
Marek Vasut