linux-kernel - Re: [RFC PATCH] nvmem: core: add sysfs cell write support

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Date: Mon, 19 Feb 2024 12:04:14 +0100
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Marco Felsch <m.felsch@...gutronix.de>
Cc: Michael Walle <michael@...le.cc>, srinivas.kandagatla@...aro.org,
 gregkh@...uxfoundation.org, rafal@...ecki.pl, linux-kernel@...r.kernel.org,
 kernel@...gutronix.de
Subject: Re: [RFC PATCH] nvmem: core: add sysfs cell write support

Hi Marco,

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

> Hi Michael,
> 
> On 24-02-16, Michael Walle wrote:
> > Hi,
> > 
> > On Thu Feb 15, 2024 at 10:14 PM CET, Marco Felsch wrote:  
> > > @@ -432,6 +466,7 @@ static int nvmem_populate_sysfs_cells(struct nvmem_device *nvmem)
> > >  	struct bin_attribute **cells_attrs, *attrs;
> > >  	struct nvmem_cell_entry *entry;
> > >  	unsigned int ncells = 0, i = 0;
> > > +	umode_t mode;
> > >  	int ret = 0;
> > >  
> > >  	mutex_lock(&nvmem_mutex);
> > > @@ -456,15 +491,18 @@ static int nvmem_populate_sysfs_cells(struct nvmem_device *nvmem)
> > >  		goto unlock_mutex;
> > >  	}
> > >  
> > > +	mode = 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 = devm_kasprintf(&nvmem->dev, GFP_KERNEL,
> > >  						    "%s@%x", entry->name,
> > >  						    entry->offset);
> > > -		attrs[i].attr.mode = 0444;  
> > 
> > cells are not writable if there is a read post process hook, see
> > __nvmem_cell_entry_write().
> > 
> > if (entry->read_post_processing)
> > 	mode &= ~0222;  
> 
> 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,
Miquèl