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Date:   Thu, 20 Jul 2023 16:03:22 +0200
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Subject: Re: [RFC PATCH 3/6] block: add new genhd flag GENHD_FL_NO_NVMEM
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To:     Daniel Golle <daniel@makrotopia.org>
Cc:     Jens Axboe <axboe@kernel.dk>, Ulf Hansson <ulf.hansson@linaro.org>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Dave Chinner <dchinner@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        =?UTF-8?Q?Thomas_Wei=c3=9fschuh?= <linux@weissschuh.net>,
        Jan Kara <jack@suse.cz>, Damien Le Moal <dlemoal@kernel.org>,
        Ming Lei <ming.lei@redhat.com>, Min Li <min15.li@samsung.com>,
        Christian Loehle <CLoehle@hyperstone.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Jack Wang <jinpu.wang@ionos.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Yeqi Fu <asuk4.q@gmail.com>, Avri Altman <avri.altman@wdc.com>,
        Hans de Goede <hdegoede@redhat.com>,
        Ye Bin <yebin10@huawei.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mmc@vger.kernel.org, linux-mtd@lists.infradead.org
References: <cover.1689802933.git.daniel@makrotopia.org>
 <96510d925cb0ca1a3a132f8f8affd4bbdafd8fc9.1689802933.git.daniel@makrotopia.org>
 <0592e021-237d-6d41-7faf-e5b93aefbeea@suse.de>
 <ZLk6-aARrlAGenk3@makrotopia.org>
From:   Hannes Reinecke <hare@suse.de>
In-Reply-To: <ZLk6-aARrlAGenk3@makrotopia.org>
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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@makrotopia.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.
> 
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