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Date: Mon, 19 Feb 2024 12:04:14 +0100
From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Marco Felsch <m.felsch@pengutronix.de>
Cc: Michael Walle <michael@walle.cc>, srinivas.kandagatla@linaro.org,
 gregkh@linuxfoundation.org, rafal@milecki.pl, linux-kernel@vger.kernel.org,
 kernel@pengutronix.de
Subject: Re: [RFC PATCH] nvmem: core: add sysfs cell write support
Message-ID: <20240219120414.32395299@xps-13>
In-Reply-To: <20240216100750.zxl4wncbgpulr2cc@pengutronix.de>
References: <20240215211401.1201004-1-m.felsch@pengutronix.de>
	<CZ6DFL6061FS.2WMDPMSSBXX8S@walle.cc>
	<20240216100750.zxl4wncbgpulr2cc@pengutronix.de>
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Hi Marco,

m.felsch@pengutronix.de wrote on Fri, 16 Feb 2024 11:07:50 +0100:

> Hi Michael,
>=20
> On 24-02-16, Michael Walle wrote:
> > Hi,
> >=20
> > On Thu Feb 15, 2024 at 10:14 PM CET, Marco Felsch wrote: =20
> > > @@ -432,6 +466,7 @@ static int nvmem_populate_sysfs_cells(struct nvme=
m_device *nvmem)
> > >  	struct bin_attribute **cells_attrs, *attrs;
> > >  	struct nvmem_cell_entry *entry;
> > >  	unsigned int ncells =3D 0, i =3D 0;
> > > +	umode_t mode;
> > >  	int ret =3D 0;
> > > =20
> > >  	mutex_lock(&nvmem_mutex);
> > > @@ -456,15 +491,18 @@ static int nvmem_populate_sysfs_cells(struct nv=
mem_device *nvmem)
> > >  		goto unlock_mutex;
> > >  	}
> > > =20
> > > +	mode =3D nvmem_bin_attr_get_umode(nvmem);
> > > +
> > >  	/* Initialize each attribute to take the name and size of the cell =
*/
> > >  	list_for_each_entry(entry, &nvmem->cells, node) {
> > >  		sysfs_bin_attr_init(&attrs[i]);
> > >  		attrs[i].attr.name =3D devm_kasprintf(&nvmem->dev, GFP_KERNEL,
> > >  						    "%s@%x", entry->name,
> > >  						    entry->offset);
> > > -		attrs[i].attr.mode =3D 0444; =20
> >=20
> > cells are not writable if there is a read post process hook, see
> > __nvmem_cell_entry_write().
> >=20
> > if (entry->read_post_processing)
> > 	mode &=3D ~0222; =20
>=20
> good point, thanks for the hint :) I will add this and send a non-rfc
> version if write-support is something you would like to have.

I like the idea but, what about mtd devices (and soon maybe UBI
devices)? This may only work on EEPROM-like devices I guess, where each
area is fully independent and where no erasure is actually expected.

Thanks,
Miqu=C3=A8l