Re: [PATCH v6] mtd: handle partitioning on devices with 0 erasesize

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Fri,  9 Jun 2017 15:58:31 +1200
Chris Packham <chris.packham@alliedtelesis.co.nz> wrote:

> erasesize is meaningful for flash devices but for SRAM there is no
> concept of an erase block so erasesize is set to 0. When partitioning
> these devices instead of ensuring partitions fall on erasesize
> boundaries we ensure they fall on writesize boundaries.
> 
> Helped-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>

Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>

> ---
> Changes in v3:
> - new
> Changes in v4:
> - None
> Changes in v5:
> - None (yet). There is some active discussion on this so it may change.
>   patch 4/5 is somewhat dependent on this but only if partitions are
>   specified on the dt node.
>   Changes in v6:
> - Use MTD_NO_ERASE flag to decide whether to use writesize or erasesize
>   for alignment purposes
> 
>  drivers/mtd/mtdpart.c | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
> index ea5e5307f667..2e152e53ace0 100644
> --- a/drivers/mtd/mtdpart.c
> +++ b/drivers/mtd/mtdpart.c
> @@ -393,8 +393,12 @@ static struct mtd_part *allocate_partition(struct mtd_info *master,
>  			const struct mtd_partition *part, int partno,
>  			uint64_t cur_offset)
>  {
> +	int wr_alignment = (master->flags & MTD_NO_ERASE) ? master->writesize:
> +							    master->erasesize;
>  	struct mtd_part *slave;
> +	u32 remainder;
>  	char *name;
> +	u64 tmp;
>  
>  	/* allocate the partition structure */
>  	slave = kzalloc(sizeof(*slave), GFP_KERNEL);
> @@ -499,10 +503,11 @@ static struct mtd_part *allocate_partition(struct mtd_info *master,
>  	if (slave->offset == MTDPART_OFS_APPEND)
>  		slave->offset = cur_offset;
>  	if (slave->offset == MTDPART_OFS_NXTBLK) {
> +		tmp = cur_offset;
>  		slave->offset = cur_offset;
> -		if (mtd_mod_by_eb(cur_offset, master) != 0) {
> -			/* Round up to next erasesize */
> -			slave->offset = (mtd_div_by_eb(cur_offset, master) + 1) * master->erasesize;
> +		remainder = do_div(tmp, wr_alignment);
> +		if (remainder) {
> +			slave->offset += wr_alignment - remainder;
>  			printk(KERN_NOTICE "Moving partition %d: "
>  			       "0x%012llx -> 0x%012llx\n", partno,
>  			       (unsigned long long)cur_offset, (unsigned long long)slave->offset);
> @@ -567,19 +572,22 @@ static struct mtd_part *allocate_partition(struct mtd_info *master,
>  		slave->mtd.erasesize = master->erasesize;
>  	}
>  
> -	if ((slave->mtd.flags & MTD_WRITEABLE) &&
> -	    mtd_mod_by_eb(slave->offset, &slave->mtd)) {
> +	tmp = slave->offset;
> +	remainder = do_div(tmp, wr_alignment);
> +	if ((slave->mtd.flags & MTD_WRITEABLE) && remainder) {
>  		/* Doesn't start on a boundary of major erase size */
>  		/* FIXME: Let it be writable if it is on a boundary of
>  		 * _minor_ erase size though */
>  		slave->mtd.flags &= ~MTD_WRITEABLE;
> -		printk(KERN_WARNING"mtd: partition \"%s\" doesn't start on an erase block boundary -- force read-only\n",
> +		printk(KERN_WARNING"mtd: partition \"%s\" doesn't start on an erase/write block boundary -- force read-only\n",
>  			part->name);
>  	}
> -	if ((slave->mtd.flags & MTD_WRITEABLE) &&
> -	    mtd_mod_by_eb(slave->mtd.size, &slave->mtd)) {
> +
> +	tmp = slave->mtd.size;
> +	remainder = do_div(tmp, wr_alignment);
> +	if ((slave->mtd.flags & MTD_WRITEABLE) && remainder) {
>  		slave->mtd.flags &= ~MTD_WRITEABLE;
> -		printk(KERN_WARNING"mtd: partition \"%s\" doesn't end on an erase block -- force read-only\n",
> +		printk(KERN_WARNING"mtd: partition \"%s\" doesn't end on an erase/write block -- force read-only\n",
>  			part->name);
>  	}
>