[PATCH RESEND u-boot-spi 8/8] mtd: mtdpart: Make mtdpart's _erase method sane

[Simon Glass]

On Wed, 14 Jul 2021 at 17:51, Marek Behún <marek.behun at nic.cz> wrote:
>
> The _erase() method of the mtdpart driver, part_erase(), currently
> implements offset shifting (for given mtdpart partition) in a weird way:
>   1. part_erase() adds partition offset to block address
>   2. parent driver's _erase() method is called
>   3. parent driver's _erase() method calls mtd_erase_callback()
>   4. mtd_erase_callback() subtracts partition offset from block address
>      so that the callback function is given correct address
> The problem here is that if the parent's driver does not call
> mtd_erase_callback() in some scenario (this was recently a case for
> spi_nor_erase(), which did not call mtd_erase_callback() at all), the
> offset is not shifted back.
>
> Moreover the code would be more readable if part_erase() not only added
> partition offset before calling parent's _erase(), but also subtracted
> it back afterwards. Currently the mtd_erase_callback() is expected to do
> this subtracting since it does have to do it anyway.
>
> Add the more steps to this procedure:
>   5. mtd_erase_callback() adds partition offset to block address so that
>      it returns the the erase_info structure members as it received them
>   6. part_erase() subtracts partition offset from block address
>
> This makes the code more logical and also prevents errors in case
> parent's driver does not call mtd_erase_callback() for some reason.
>
> (BTW, the purpose of mtd_erase_callback() in Linux is to inform the
>  caller that it is done, since in Linux erasing is done asynchronously.
>  We are abusing the purpose of mtd_erase_callback() in U-Boot for
>  completely different purpose. The callback function itself has empty
>  implementation in all cases in U-Boot.)
>
> Signed-off-by: Marek Behún <marek.behun at nic.cz>
> Tested-by: Masami Hiramatsu <masami.hiramatsu at linaro.org>
> ---
>  drivers/mtd/mtdpart.c | 26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)Reviewed-by: Simon Glass <sjg at chromium.org>
>

Reviewed-by: Simon Glass <sjg at chromium.org>