[U-Boot-Users] [PATCH V2] Round the serial port clock divisor value returned by calc_divisor()

[Jerry Van Baren]

Wolfgang Denk wrote:
> In message <1215543298-26921-1-git-send-email-hugo.villeneuve at lyrtech.com> you wrote:
>> Round the serial port clock divisor value returned by
>> calc_divisor().
>>
>> Signed-off-by: Hugo Villeneuve <hugo.villeneuve at lyrtech.com>
>> Signed-off-by: John Roberts <john.roberts at pwav.com>
>>
>> ---
>>
>> Rounding is important, especially when using high baud rates
>> values like 115200bps. When using the non-rounded value, some
>> boards will work and some won't.
>>
>>  drivers/serial/serial.c |    6 +++++-
>>  1 files changed, 5 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
>> index 76425d8..1192f07 100644
>> --- a/drivers/serial/serial.c
>> +++ b/drivers/serial/serial.c
>> @@ -144,8 +144,12 @@ static int calc_divisor (NS16550_t port)
>>  #else
>>  #define MODE_X_DIV 16
>>  #endif
>> -	return (CFG_NS16550_CLK / MODE_X_DIV / gd->baudrate);
>>  
>> +	/* Compute divisor value. Normally, we should simply return:
>> +	 *   CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate
>> +	 * but we need to round that value by adding 0.5 or 8/16.
>> +	 * Rounding is especially important at high baud rates. */
>> +	return (((16 * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate) + 8) / 16;
>>  }
> 
> Your patch causes problems with some boards:
> 
> Configuring for SBC8540 board...
> serial.c: In function 'calc_divisor':
> serial.c:153: warning: integer overflow in expression
> serial.c:153: warning: integer overflow in expression
> 
> Configuring for sbc8548 board...
> serial.c: In function 'calc_divisor':
> serial.c:153: warning: integer overflow in expression
> serial.c:153: warning: integer overflow in expression
> 
> 
> Do you have a quick fix, or shall I back out the patch?
> 
> Best regards,
> 
> Wolfgang Denk

The formula I proposed previously in this thread compiles OK.  I cannot 
verify it is correct on real hardware, however.
<http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/43499/focus=43506>

My apologies for providing the patch as an attachment.  I need to add 
the external editor plugin so I can use tbird for proper inline patches.

Best regards,
gvb

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