[U-Boot] [PATCH] spi: cadence_qspi_apb: Ensure baudrate doesn't exceed max value

[Marek Vasut]

On 08/07/2016 04:11 PM, Chin Liang See wrote:
> On Sun, 2016-08-07 at 16:05 +0200, Marek Vasut wrote:
>> On 08/07/2016 03:53 PM, Chin Liang See wrote:
>>> Ensuring the baudrate divisor value doesn't exceed the max value
>>> in the calculation.It will be capped at max value to ensure the
>>> correct value being written into the register.
>>>
>>> Signed-off-by: Chin Liang See <clsee at altera.com>
>>> Cc: Marek Vasut <marex at denx.de>
>>> Cc: Jagan Teki <jteki at openedev.com>
>>> Cc: Dinh Nguyen <dinguyen at altera.com>
>>> ---
>>>  drivers/spi/cadence_qspi_apb.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/spi/cadence_qspi_apb.c
>>> b/drivers/spi/cadence_qspi_apb.c
>>> index 1a35d55..e6a8ecb 100644
>>> --- a/drivers/spi/cadence_qspi_apb.c
>>> +++ b/drivers/spi/cadence_qspi_apb.c
>>> @@ -293,6 +293,10 @@ void cadence_qspi_apb_config_baudrate_div(void
>>> *reg_base,
>>>  	debug("%s: ref_clk %dHz sclk %dHz Div 0x%x\n", __func__,
>>>  	      ref_clk_hz, sclk_hz, div);
>>>  
>>> +	/* ensure the baud rate doesn't exceed the max value */
>>> +	if (div > CQSPI_REG_CONFIG_BAUD_MASK)
>>> +		div = CQSPI_REG_CONFIG_BAUD_MASK;
>>> +
>>>  	div = (div & CQSPI_REG_CONFIG_BAUD_MASK) <<
>>> CQSPI_REG_CONFIG_BAUD_LSB;
>>
>> The capping happens here ^ already , doesn't it ?
> 
> I have initial thought too until someone file me a bug on this. The bug
> happen when the calculated div = 16. After and with the mask, the value
> writen to register is actually 0 (register field for baudrate divisor).

So this is what the problem is all about, thanks for clarifying (and
that should be in the commit message!). But then, you don't need the
masking, it can be turned into reg = div << CQSPI_REG_CONFIG_BAUD_LSB.

-- 
Best regards,
Marek Vasut