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From:   "Daniel Walker (danielwa)" <danielwa@cisco.com>
To:     Pratyush Yadav <me@yadavpratyush.com>
CC:     Tudor Ambarus <tudor.ambarus@microchip.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Richard Weinberger <richard@nod.at>,
        "xe-linux-external(mailer list)" <xe-linux-external@cisco.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
        "Miquel Raynal" <miquel.raynal@bootlin.com>
Subject: Re: [RFC-PATCH] mtd: spi-nor: add conditional 4B opcodes
Thread-Topic: [RFC-PATCH] mtd: spi-nor: add conditional 4B opcodes
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Date:   Thu, 7 May 2020 18:13:57 +0000
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On Thu, May 07, 2020 at 11:33:46PM +0530, Pratyush Yadav wrote:
> On 07/05/20 09:20AM, Daniel Walker wrote:
> > Some chips have 4B opcodes, but there is no way to know if they have
> > them. This device tree option allows platform owners to force enable 4b
> > opcodes when they know their chips support it even when it can be
> > automatically identified.
>=20
> Do you mean that two chips might have the same ID but one of them can=20
> support 4B opcodes and the other can not? Is it possible to detect this=20
> in a fixup hook? I think it would be better to do something like this in=
=20
> a fixup hook instead of via device tree.
 =20
Yes. The chip I added the option for is an example of this, it's n25q256a. =
I'm not familiar with the
fixup hook mechanism, but I would assume you need some way to tell between =
the 4B
opcode chips and the non-4B opcode chips. For n25q256a, we have not found a=
 way
to do that.

Daniel=