[U-Boot] [PATCH v2 2/8] spi: cadence_qspi: Fix baud rate calculation

[Marek Vasut]

On 11/25/2016 04:19 PM, Phil Edworthy wrote:
> Hi Marek,
> 
> On 25 November 2016 14:58 Marek Vasut wrote:
>> On 11/25/2016 03:38 PM, Phil Edworthy wrote:
>>> With the existing code, when the requested SPI clock rate is near
>>> to the lowest 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>
>>> ---
>>> v2:
>>>  - Use the DIV_ROUND_UP macro
>>> ---
>>>  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..b9e0df7 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 = DIV_ROUND_UP(ref_clk_hz, sclk_hz);
>>> +	div = DIV_ROUND_UP(div, 2) - 1;
>>
>> Same as you did for u-boot, right ?
> Eh? This is u-boot :)

Yeah, I realized that too when I saw the later patches. I thought this
was for the CQSPI in Linux at right.


-- 
Best regards,
Marek Vasut