[PATCH RFC] mtdpart: don't force alignment to eraseblock if flags have MTD_NO_ERASE

[Boris Brezillon]

Le Fri, 14 Jul 2017 12:20:27 +0200,
Uwe Kleine-König <u.kleine-koenig at pengutronix.de> a écrit :

> Some mtd devices don't need to be erased before writing to them. For
> these it doesn't make sense to force partition alignment to erase
> blocks.
> 
> This patch allows partitioning an Everspin mr25h256 that has
> erasesize=32768, size=32768 and writesize=1.

I might be wrong but it seems this patch is more or less addressing the
problem fixed by [1].

Can you try linux-next (or l2-mtd/master)?

[1]https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/mtd/mtdpart.c?h=next-20170714&id=1eeef2d7483a7e3f8d2dd2a5b9939b3b814dc549

> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
> ---
> Hello,
> 
> this is my followup suggestion for
> 
> 	From: Bastian Stender <bst at pengutronix.de>
> 	Subject: Re: [PATCH 1/2] mtd: spi-nor: make n_sectors in flash_info 32 bit wide
> 	Message-Id: <afb06b83-e97b-48db-9875-9f76b365a5f4 at pengutronix.de>
> 
> 
> 
> It's IMHO ugly because the two bodys of the newly introduced if look very
> similar, but I think there is not much we can do about this.
> 
> To ease your reviews: The else body is exactly what we had before.
> 
> I'm a bit unsure about the check
> 
> 	slave->mtd.erasesize >= slave->mtd.writesize
> 
> because if that is false, the old code is not only inconvenient by not allowing
> partitions, but also wrong. So probably the check can safely be dropped?
> 
> Otherwise the logic should be:
> 
> 	if (MTD_NO_ERASE):
> 		alignto = writesize
> 	else:
> 		alignto = max(writesize, erasesize)
> 	    
> Best regards
> Uwe
> 
>  drivers/mtd/mtdpart.c | 47 +++++++++++++++++++++++++++++++++--------------
>  1 file changed, 33 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
> index ea5e5307f667..956c8f0ce2dd 100644
> --- a/drivers/mtd/mtdpart.c
> +++ b/drivers/mtd/mtdpart.c
> @@ -567,20 +567,39 @@ 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)) {
> -		/* 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",
> -			part->name);
> -	}
> -	if ((slave->mtd.flags & MTD_WRITEABLE) &&
> -	    mtd_mod_by_eb(slave->mtd.size, &slave->mtd)) {
> -		slave->mtd.flags &= ~MTD_WRITEABLE;
> -		printk(KERN_WARNING"mtd: partition \"%s\" doesn't end on an erase block -- force read-only\n",
> -			part->name);
> +	if (slave->mtd.flags & MTD_NO_ERASE &&
> +	    slave->mtd.erasesize >= slave->mtd.writesize) {
> +		/* If we don't need to erase, then align to writesize */
> +		if ((slave->mtd.flags & MTD_WRITEABLE) &&
> +		    mtd_mod_by_ws(slave->offset, &slave->mtd)) {
> +			/* Doesn't start on a boundary of page */
> +			/* FIXME: Can a minor erase block be smaller than a page? */
> +			slave->mtd.flags &= ~MTD_WRITEABLE;
> +			printk(KERN_WARNING"mtd: partition \"%s\" doesn't start on a page boundary -- force read-only\n",
> +			       part->name);
> +		}
> +		if ((slave->mtd.flags & MTD_WRITEABLE) &&
> +		    mtd_mod_by_ws(slave->mtd.size, &slave->mtd)) {
> +			slave->mtd.flags &= ~MTD_WRITEABLE;
> +			printk(KERN_WARNING"mtd: partition \"%s\" doesn't end on a page boundary -- force read-only\n",
> +			       part->name);
> +		}
> +	} else {
> +		if ((slave->mtd.flags & MTD_WRITEABLE) &&
> +		    mtd_mod_by_eb(slave->offset, &slave->mtd)) {
> +			/* 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",
> +			       part->name);
> +		}
> +		if ((slave->mtd.flags & MTD_WRITEABLE) &&
> +		    mtd_mod_by_eb(slave->mtd.size, &slave->mtd)) {
> +			slave->mtd.flags &= ~MTD_WRITEABLE;
> +			printk(KERN_WARNING"mtd: partition \"%s\" doesn't end on an erase block -- force read-only\n",
> +			       part->name);
> +		}
>  	}
>  
>  	mtd_set_ooblayout(&slave->mtd, &part_ooblayout_ops);