Re: [PATCH] mtd: keep original flags for every struct mtd_info

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Tue, 20 Nov 2018 09:55:45 +0100
Rafał Miłecki <zajec5@gmail.com> wrote:

> From: Rafał Miłecki <rafal@milecki.pl>
> 
> When allocating a new partition mtd subsystem runs internal tests in the
> allocate_partition(). They may result in modifying specified flags (e.g.
> dropping some /features/ like write access).
> 
> Those constraints don't have to be necessary true for subpartitions. It
> may happen parent partition isn't block aligned (effectively disabling
> write access) while subpartition may fit blocks nicely. In such case all
> checks should be run again (starting with original flags value).
> 
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> ---
>  drivers/mtd/mtdcore.c   | 2 ++
>  drivers/mtd/mtdpart.c   | 3 ++-
>  include/linux/mtd/mtd.h | 1 +
>  3 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 97ac219c082e..2d24701255e5 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -665,6 +665,8 @@ static void mtd_set_dev_defaults(struct mtd_info *mtd)
>  	} else {
>  		pr_debug("mtd device won't show a device symlink in sysfs\n");
>  	}
> +
> +	mtd->orig_flags = mtd->flags;
>  }
>  
>  /**
> diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
> index 99c460facd5e..2b6e53af47da 100644
> --- a/drivers/mtd/mtdpart.c
> +++ b/drivers/mtd/mtdpart.c
> @@ -346,7 +346,8 @@ static struct mtd_part *allocate_partition(struct mtd_info *parent,
>  
>  	/* set up the MTD object for this partition */
>  	slave->mtd.type = parent->type;
> -	slave->mtd.flags = parent->flags & ~part->mask_flags;
> +	slave->mtd.flags = parent->orig_flags & ~part->mask_flags;
> +	slave->mtd.orig_flags = slave->mtd.flags;
>  	slave->mtd.size = part->size;
>  	slave->mtd.writesize = parent->writesize;
>  	slave->mtd.writebufsize = parent->writebufsize;
> diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
> index cd0be91bdefa..b491a08e87e5 100644
> --- a/include/linux/mtd/mtd.h
> +++ b/include/linux/mtd/mtd.h
> @@ -207,6 +207,7 @@ struct mtd_debug_info {
>  struct mtd_info {
>  	u_char type;
>  	uint32_t flags;
> +	uint32_t orig_flags; /* Flags as before running mtd checks */

Hm, I'm not a big fan of this orig_flags field. I'd prefer to have
Miquel's patch series [1] ported to Linus, so that master can be
retrieved with a simple loop:

struct mtd_info *mtd_get_master(struct mtd_info *mtd)
{
	struct mtd_info *master = mtd;

	while (master->parent)
		master = master->parent;
}

[1]https://www.mail-archive.com/u-boot@lists.denx.de/msg297465.html