linux-kernel - Re: [RFC PATCH 3/6] block: add new genhd flag GENHD_FL_NO

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Date:   Thu, 20 Jul 2023 14:47:37 +0100
From:   Daniel Golle <daniel@...rotopia.org>
To:     Hannes Reinecke <hare@...e.de>
Cc:     Jens Axboe <axboe@...nel.dk>, Ulf Hansson <ulf.hansson@...aro.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Dave Chinner <dchinner@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Weißschuh <linux@...ssschuh.net>,
        Jan Kara <jack@...e.cz>, Damien Le Moal <dlemoal@...nel.org>,
        Ming Lei <ming.lei@...hat.com>, Min Li <min15.li@...sung.com>,
        Christian Loehle <CLoehle@...erstone.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jack Wang <jinpu.wang@...os.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Yeqi Fu <asuk4.q@...il.com>, Avri Altman <avri.altman@....com>,
        Hans de Goede <hdegoede@...hat.com>,
        Ye Bin <yebin10@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafał Miłecki <rafal@...ecki.pl>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-mtd@...ts.infradead.org
Subject: Re: [RFC PATCH 3/6] block: add new genhd flag GENHD_FL_NO_NVMEM

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@...rotopia.org>
> > ---
> >   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.

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.