[U-Boot] flash erasing: len alignment

[Wolfgang Denk]

Dear Mike Frysinger,

In message <200812110431.35694.vapier at gentoo.org> you wrote:
> 
> the different flash subsystems dont exactly all operate the same, specifically 
> when it comes to erasing.  some require you to specify lengths that are 
> aligned exactly to the erase sector size whereas others are much more 
> intelligent: they automatically round up for you.  is there any real arguments 
> for a particular method ?

Flash commands *should* support two formats:

1) sector (and bank) numbers, for example:

	erase 1:3-6

2) start and end address, for example:

	erase 40000000 4003FFFF

3) start address and length, for example:

	erase 40000000 +40000

The idea is that addresses (start and end address) have to  be  exact
and  match  sector  boundaries  as  needed by the flash device, while
length is handled intelligently, i. e. to erase one  sector  you  can
write

	erase 40000000 +1

Sector and bank numbers have to be exact, too, of course.

> personally, i prefer the latter behavior as it makes scripting a hell of a lot 
> easier.  for example, if i want to load a binary file into a flash, the 
> loading process (i.e. tftp) will automatically set $(filesize) which i can 
> then use as the erase/write length.  otherwise i need to either manually do 
> the rounding up based on sector size, or i have to assume ahead of time that 
> the file will never exceed a certain max size and use that hardcoded value 
> (which leads to wasted time erasing sectors that never actually get used and 
> unable to use the same code across multiple platforms).

That's why the "+length" method was added.

> here's an example change to the SPI flash driver:
> --- a/u-boot-2008.10/drivers/mtd/spi/stmicro.c
> +++ b/u-boot-2008.10/drivers/mtd/spi/stmicro.c
> @@ -262,12 +262,12 @@ int stmicro_erase(struct spi_flash
>  
>  	sector_size = stm->params->page_size * stm->params->pages_per_sector;
>  
> -	if (offset % sector_size || len % sector_size) {
> +	if (offset % sector_size) {
>  		debug("SF: Erase offset/length not multiple of sector size\n");
>  		return -1;
>  	}
>  
> -	len /= sector_size;
> +	len = len / sector_size + !!(len % sector_size);

Except for the notation, which I find not so easy to read, that's OK
with me. Is a documentation update needed?

Best regards,

Wolfgang Denk

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