[U-Boot] [PATCH 2/7] spi: cadence_qspi: Fix baud rate calculation

[Phil Edworthy]

Hi Marek,

On 02 November 2016 19:39, Marek Vasut wrote:
> On 11/02/2016 04:15 PM, Phil Edworthy wrote:
> > With the existing code, when the requested SPI clock rate is near
> > to the lowerest that can be achieved by the hardware (max divider
> > of the ref clock is 32), the generated clock rate is wrong.
> > For example, with a 50MHz ref clock, when asked for anything less
> > than a 1.5MHz SPI clock, the code sets up the divider to generate
> > 25MHz.
> >
> > This change fixes the calculation.
> >
> > Signed-off-by: Phil Edworthy <phil.edworthy at renesas.com>
> > ---
> >  drivers/spi/cadence_qspi_apb.c | 23 +++++++----------------
> >  1 file changed, 7 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/spi/cadence_qspi_apb.c b/drivers/spi/cadence_qspi_apb.c
> > index 2403e71..71bde1f 100644
> > --- a/drivers/spi/cadence_qspi_apb.c
> > +++ b/drivers/spi/cadence_qspi_apb.c
> > @@ -273,22 +273,13 @@ void cadence_qspi_apb_config_baudrate_div(void
> *reg_base,
> >  	reg = readl(reg_base + CQSPI_REG_CONFIG);
> >  	reg &= ~(CQSPI_REG_CONFIG_BAUD_MASK <<
> CQSPI_REG_CONFIG_BAUD_LSB);
> >
> > -	div = ref_clk_hz / sclk_hz;
> > -
> > -	if (div > 32)
> > -		div = 32;
> > -
> > -	/* Check if even number. */
> > -	if ((div & 1)) {
> > -		div = (div / 2);
> > -	} else {
> > -		if (ref_clk_hz % sclk_hz)
> > -			/* ensure generated SCLK doesn't exceed user
> > -			specified sclk_hz */
> > -			div = (div / 2);
> > -		else
> > -			div = (div / 2) - 1;
> > -	}
> > +	/*
> > +	 * The baud_div field in the config reg is 4 bits, and the ref clock is
> > +	 * divided by 2 * (baud_div + 1). Round up the divider to ensure the
> > +	 * SPI clock rate is less than or equal to the requested clock rate.
> > +	 */
> > +	div = (ref_clk_hz + sclk_hz - 1) / sclk_hz;
> 
> DIV_ROUND_UP()
Ah yes, that would be clearer!

> > +	div = ((div + 1) / 2) - 1;
> Is this roundup() ?
It's DIV_ROUND_UP() - 1

> 
> >  	debug("%s: ref_clk %dHz sclk %dHz Div 0x%x\n", __func__,
> >  	      ref_clk_hz, sclk_hz, div);
> >
> 
> 
> --
> Best regards,
> Marek Vasut

Thanks
Phil