Re: [PATCH 3/8] block: add new genhd flag GENHD_FL_NVMEM

[Daniel Golle <daniel@makrotopia.org>]

On Fri, Mar 22, 2024 at 10:49:48AM -0700, Bart Van Assche wrote:
> On 3/21/24 12:33, Daniel Golle wrote:
> > Add new flag to destinguish block devices which may act as an NVMEM
> > provider.
> > 
> > Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> > ---
> >   include/linux/blkdev.h | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> > index c3e8f7cf96be9..f2c4f280d7619 100644
> > --- a/include/linux/blkdev.h
> > +++ b/include/linux/blkdev.h
> > @@ -81,11 +81,13 @@ struct partition_meta_info {
> >    * ``GENHD_FL_NO_PART``: partition support is disabled.  The kernel will not
> >    * scan for partitions from add_disk, and users can't add partitions manually.
> >    *
> > + * ``GENHD_FL_NVMEM``: the block device should be considered as NVMEM provider.
> >    */
> >   enum {
> >   	GENHD_FL_REMOVABLE			= 1 << 0,
> >   	GENHD_FL_HIDDEN				= 1 << 1,
> >   	GENHD_FL_NO_PART			= 1 << 2,
> > +	GENHD_FL_NVMEM				= 1 << 3,
> >   };
> 
> What would break if this flag wouldn't exist?

As both, MTD and UBI already act as NVMEM providers themselves, once
the user creates a ubiblock device or got CONFIG_MTD_BLOCK=y set in their
kernel configuration, we would run into problems because both, the block
layer as well as MTD or UBI would try to be an NVMEM provider for the same
device tree node.

I intially suggested the invert of this flag, GENHD_FL_NO_NVMEM which
would be set only for mtdblock and ubiblock devices to opt-out of acting
as NVMEM proviers. However, in a previous comment [1] on the RFC it was
requested to make this opt-in instead.

[1]: https://patchwork.kernel.org/comment/25432948/