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

[Hannes Reinecke <hare@suse.de>]

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