linux-kernel - Re: [PATCH v16 00/15] mtd: spi-nor: add xSPI Octal DTR support

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Message-ID: <d9d96eda-4cb6-fe68-7469-e73dc7ba2fda@microchip.com>
Date:   Wed, 28 Oct 2020 15:21:02 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <p.yadav@...com>
CC:     <miquel.raynal@...tlin.com>, <richard@....at>, <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <nsekhar@...com>, <boris.brezillon@...labora.com>
Subject: Re: [PATCH v16 00/15] mtd: spi-nor: add xSPI Octal DTR support

On 10/28/20 2:49 PM, Pratyush Yadav wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Hi Tudor,
> 
> On 28/10/20 07:53AM, Tudor.Ambarus@...rochip.com wrote:
>> Hi, Pratyush,
>>
>> On 10/5/20 6:31 PM, Pratyush Yadav wrote:
>>> Tested on Micron MT35X and S28HS flashes for Octal DTR.
>>
>> Do these flashes define the "Command Sequences to Change to
>> Octal DDR (8D-8D-8D) mode" table? Can't we use that table
>> instead of defining our own octal dtr enable functions?
> 
> The Micron flash does not have this table. The Cypress flash does. The
> problem is that one of the samples of the Cypress flash I tested on had
> incorrect data in that table which meant the sequence would fail. The
> newer samples of the flash have the correct data.

Can we differentiate the Cypress flashes? Do you remember what
was the incorrect data?

> 
> I don't know how many of those faulty flashes are out there in the wild.
> IMO, to be on the safe side spi_nor_cypress_octal_dtr_enable() needs to
> be implemented. So from the point of view of this series there is no
> need to parse the Octal DDR enable table.

Meh, we cover manufacturer's mistakes. On the long run, our aim should be
to follow the SFDP standard and if a flash implements it wrong, to either
fix it via a fixup hook (if the fix is minimal), or to skip the faulty
table.

Regarding "Command Sequences to Change to Octal DDR (8D-8D-8D) mode"
table. Have you looked over
https://patchwork.ozlabs.org/project/linux-mtd/patch/1590737775-4798-4-git-send-email-masonccyang@mxic.com.tw/
?
Is there a standard way to determine the offsets of opcode, addr and
data in the cmd seq?

Cheers,
ta
> 
>> I see that Mason used this table for a macronix flash:
>> https://patchwork.ozlabs.org/project/linux-mtd/patch/1590737775-4798-4-git-send-email-masonccyang@mxic.com.tw/
>> https://patchwork.ozlabs.org/project/linux-mtd/patch/1590737775-4798-8-git-send-email-masonccyang@mxic.com.tw/
>>
>> Cheers,
>> ta
> 
> --
> Regards,
> Pratyush Yadav
> Texas Instruments India
>