Re: [RFC PATCH 3/6] block: add new genhd flag GENHD_FL_NO_NVMEM

[Hannes Reinecke]

On 7/20/23 15:47, Daniel Golle wrote:
> On Thu, Jul 20, 2023 at 10:24:18AM +0200, Hannes Reinecke wrote:
> > On 7/20/23 00:03, Daniel Golle wrote:
> > > Add new flag to destinguish block devices which should not act as an
> > > NVMEM provider, such as for example an emulated block device on top of
> > > an MTD partition which already acts as an NVMEM provider itself.
> > >
> > > Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>
> > > ---
> > >    include/linux/blkdev.h | 3 +++
> > >    1 file changed, 3 insertions(+)
> > >
> > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> > > index 2f5371b8482c0..e853d1815be15 100644
> > > --- a/include/linux/blkdev.h
> > > +++ b/include/linux/blkdev.h
> > > @@ -80,11 +80,14 @@ 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_NO_NVMEM``: NVMEM emulation is disabled.  The kernel will not
> > > + * emulate an NVMEM device on top of this disk.
> > >     */
> > >    enum {
> > >    	GENHD_FL_REMOVABLE			= 1 << 0,
> > >    	GENHD_FL_HIDDEN				= 1 << 1,
> > >    	GENHD_FL_NO_PART			= 1 << 2,
> > > +	GENHD_FL_NO_NVMEM			= 1 << 3,
> > >    };
> > >    enum {
> > Please reverse this flag. Most of the devices will not have an NVMEM
> > partition, and we shouldn't require each and every driver to tag their
> > devices.
> > So please use GENHD_FL_NVMEM and only set this flag on devices which really
> > have an NVMEM partition.
>
> The idea here was to exclude all those devices which already implement
> an NVMEM provider on a lower layer themselves, such as MTD.
> In this cases it would be ambigous if the OF node represents the
> NVMEM device registered by the MTD framework or if blk-nvmem should be
> used.
Hmm; not sure if I follow.
In the end, it doesn't really matter whether you check for
GENHD_FL_NO_NVMEM or !GENHD_FL_NVMEM.
With the difference being that in the former case you have to
tag 99% of all existing block devices, and in the latter you
have to tag 1%.

> In all other cases device tree can unambigously indicate whether a
> block device should serve as NVMEM provider (and right, most of them
> never will).
>
> However, reversing the logic seems fine just as well.

Thanks. Please do.

Cheers,

Hannes