Re: [PATCH 1/2] dt-bindings: mtd: spi-nor: document new flag

From: Vignesh Raghavendra <vigneshr@ti.com>
To: Michael Walle <michael@walle.cc>,
	Tudor Ambarus <tudor.ambarus@microchip.com>
Cc: <linux-mtd@lists.infradead.org>, <devicetree@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH 1/2] dt-bindings: mtd: spi-nor: document new flag
Date: Thu, 19 Dec 2019 11:03:33 +0530	[thread overview]
Message-ID: <2dfc30a7-3261-d783-8256-f72458a0141b@ti.com> (raw)
In-Reply-To: <af3692dba69e85fa8136ab3d170bef39@walle.cc>

Hi Michael,

[...]
>>> +- no-unlock : By default, linux unlocks the whole flash because there
>>> +           are legacy flash devices which are locked by default
>>> +           after reset. Set this flag if you don't want linux to
>>> +           unlock the whole flash automatically. In this case you
>>> +           can control the non-volatile bits by the
>>> +           flash_lock/flash_unlock tools.
>>>
>>
>> Current SPI NOR framework unconditionally unlocks entire flash which
>> I agree is not the best thing to do, but I don't think we need
>> new DT property here. MTD cmdline partitions and DT partitions already
>> provide a way to specify that a partition should remain locked[1][2]
> 
> I know that the MTD layer has the same kind of unlocking. But that
> unlocking is done on a per mtd partition basis. Eg. consider something
> like the following
> 
>  mtd1 bootloader  (locked)
>  mtd2 firmware    (locked)
>  mtd3 kernel
>  mtd4 environment
> 
> Further assume, that the end of mtd2 aligns with one of the possible
> locking areas which are supported by the flash chip. Eg. the first quarter.
> 
> The mtd layer would do two (or four, if "lock" property is set) unlock()
> calls, one for mtd1 and one for mtd2.
> 

> My point here is, that the mtd partitions doesn't always map to the
> locking regions of the SPI flash (at least if the are not merged together).
> 

You are right! This will be an issue if existing partitions are not
aligned to locking regions.

I take my comments back... But I am not sure if a new DT property is the
needed. This does not describe HW and is specific to Linux SPI NOR
stack. How about a module parameter instead?
Module parameter won't provide per flash granularity in controlling
unlocking behavior. But I don't think that matters.

Tudor,

You had a patch doing something similar. Does module param sound good to
you?

-- 
Regards
Vignesh