linux-kernel - Re: [PATCH 4/8] mtd: spi-nor: disallow further writes to SR if WP# is low

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Message-ID: <20160129192341.GD19540@google.com>
Date:	Fri, 29 Jan 2016 11:23:41 -0800
From:	Brian Norris <computersforpeace@...il.com>
To:	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Rafał Miłecki <zajec5@...il.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bayi Cheng <bayi.cheng@...iatek.com>,
	Marek Vasut <marex@...x.de>,
	Daniel Kurtz <djkurtz@...omium.org>
Subject: Re: [PATCH 4/8] mtd: spi-nor: disallow further writes to SR if WP#
 is low

On Fri, Jan 29, 2016 at 10:22:34AM -0300, Ezequiel Garcia wrote:
> On 28 January 2016 at 16:48, Brian Norris <computersforpeace@...il.com> wrote:
> > On Thu, Jan 28, 2016 at 04:24:50PM -0300, Ezequiel Garcia wrote:
> >> How about this:
> >>
> >> 1) ioctl(MEMLOCK) the entire flash (SR_SRWD is set)
> >> 2) ioctl(MEMUNLOCK) partially (SW_SRWD keeps set)
> >> 3) ioctl(MEMLOCK) the entire flash again

...

> >> but would (3)  be allowed given
> >> SW_SRWD is set?
> >
> > Yes, if /WP=1 (high).
> >
> 
> Right. So, after giving some more thought do this, I'd say it might
> make sense to clear SRWD only when unlocking the entire flash. If
> anything else, it would allow a path to disable hardware protection on
> the lock range?

Yes, that sounds fine to me, as it does allow removal of the HW
protection. So one could, for example, do:

0. bring /WP=1 (high)
1. unlock the whole flash
2. bring /WP=0 (low) -- flash is still unlocked
3. allow a one-time relocking of the flash via MEMLOCK
4. no more locking changes

I'll send out v2.

Brian