MTD with non-power-of-2 page size

Dave Kitchen at
Wed Aug 19 07:29:21 PDT 2015

Hi Sascha

Thank you for the hint. I now have running code with the non-power-of-2 
page size.
Shall I try and generate/submit a patch for this? The code may be 
marginally slower in the power-of-2 case than the original, but I defy 
anyone to notice if they are using spi boot!


On 19/08/15 15:20, Sascha Hauer wrote:
> Hi Dave,
> On Wed, Aug 12, 2015 at 12:21:00PM +0100, Dave Kitchen wrote:
>> I have just started to work with barebox on an Atmel at91sam9g45 processor.
>> The board has an Atmel AT45DB161 dataflash configured as 528-byte page size.
>> I find that eg saveenv command does not run as the page erase fails
>> with EINVAL. On tracing this is fired from the page size and offset
>> correction code [mtd/core,c mtd_erase_align()] which uses bit
>> masking to align the size and offset. Unfortunately bit-masking does
>> not work with non-power-of-2 pages. Has anyone else addressed this
>> problem?
>> The 'trivial' exercise of replacing the bit masks by modulo [%]
>> operator does not succeed as the compiler I am using (gcc!) does not
>> support long-long divmod.
> You could use do_div here which returns the remainder. Also see the
> mtd_div_by_eb() and mtd_mod_by_eb() functions which may be what you are
> looking for.
> Sascha

Dave Kitchen
InSync technology Ltd
Tilbrook House
2-4 Grenehurst Way
GU31 4AZ
+44(0) 1730 235117

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