linux-kernel - Re: [PATCH] mtd: spi-nor: Add 4B

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Date:   Tue, 21 Apr 2020 04:52:01 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <danielwa@...co.com>
CC:     <xe-linux-external@...co.com>, <miquel.raynal@...tlin.com>,
        <richard@....at>, <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mtd: spi-nor: Add 4B_OPCODES flag to n25q256a

On Monday, April 20, 2020 7:25:51 PM EEST Daniel Walker (danielwa) wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
> content is safe
> On Mon, Apr 20, 2020 at 03:45:59PM +0000, Tudor.Ambarus@...rochip.com wrote:
> > Hi, Daniel,
> > 
> > On Friday, April 17, 2020 8:46:19 PM EEST Daniel Walker wrote:
> > > EXTERNAL EMAIL: Do not click links or open attachments unless you know
> > > the
> > > content is safe
> > > 
> > > The n25q256a supports 4-byte opcodes so lets add the flag.
> > 
> > This is not true for all the n25q256a flashes. SPINOR_OP_PP_4B,
> > SPINOR_OP_BE_4K_4B and SPINOR_OP_SE_4B are valid just for the part numbers
> > N25Q256A83ESF40x, N25Q256A83E1240x, and N25Q256A83ESFA0F.
> > 
> > You need to differentiate between the aforementioned flashes and the rest
> > in the n25q256a, in order to add the 4-byte opcodes flag.
> 
> How do you suggest I do that ? Can I add a new entry into this table with
> more specific information about the chips ?
> 

We need to find a differentiator at runtime. If we are lucky, there might be 
some SFDP changes between the 4-byte opcodes capable flashes and the rest. 
Please dump all the sfdp tables, we can start from there. There's a thread 
that might interest you, see http://u-boot.10912.n7.nabble.com/Regressions-in-MTD-SPI-FLASH-td382956.html#a383126.

A more elegant way to solve it, is by parsing the 4bait sfdp table, but I 
haven't checked if this flash supports it or not. Anyway, not something that 
we can control, the manufacturer should add it.

Cheers,
ta