Date:   Mon, 20 Dec 2021 15:46:41 +0530
From:   Pratyush Yadav <p.yadav@ti.com>
To:     <Tudor.Ambarus@microchip.com>
CC:     <michael@walle.cc>, <vigneshr@ti.com>, <miquel.raynal@bootlin.com>,
        <richard@nod.at>, <linux-mtd@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <Nicolas.Ferre@microchip.com>,
        <zhengxunli@mxic.com.tw>, <jaimeliao@mxic.com.tw>
Subject: Re: [PATCH v2 2/2] mtd: spi-nor: macronix: Add support for
 mx66lm1g45g
Message-ID: <20211220101639.ycdz4twnhhp5bvlj@ti.com>
References: <20211209190436.401946-1-tudor.ambarus@microchip.com>
 <20211209190436.401946-2-tudor.ambarus@microchip.com>
 <20211217113810.mzqrwf6vxfniggn3@ti.com>
 <c94a306d-a71f-6465-bb3d-d9e6ae55148b@microchip.com>
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Hi Tudor,

On 17/12/21 12:38PM, Tudor.Ambarus@microchip.com wrote:
> On 12/17/21 1:38 PM, Pratyush Yadav wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > On 09/12/21 09:04PM, Tudor Ambarus wrote:
> >> mx66lm1g45g supports just 1-1-1, 8-8-8 and 8d-8d-8d modes. There are
> >> versions of mx66lm1g45g which do not support SFDP, thus use
> >> SPI_NOR_SKIP_SFDP. The RDID command issued through the octal peripheral
> >> interface outputs data always in STR mode for whatever reason. Since
> > 
> > Huh! I hope this is a mistake from the chip designers, because if it
> > isn't they need a stern talking-to ;-)
> > 
> >> 8d-8d-8s is not common, avoid reading the ID when enabling the octal dtr
> >> mode. Instead, read back the CR2 to check if the switch was successful.
> >> Tested in 1-1-1 and 8d-8d-8d modes using sama7g5 QSPI IP.
> > 
> > Datasheet?
> 
> MX66LM1G45G datasheet:
> https://www.macronix.com/Lists/Datasheet/Attachments/7929/MX66LM1G45G,%203V,%201Gb,%20v1.1.pdf

Thanks.

I see that the RDID waveform holds each byte of the ID for a whole clock 
cycle. So you would read ab ab cd cd ef ef. I've seen this before 
somewhere, and sure enough, digging through my inbox I've found this 
patch [0]. In this read ID is performed but only alternate bytes are 
compared since they are repeated. I think you should do the same. I feel 
like reading/comparing 3 bytes is more "robust".

BTW, this patch series also adds support for mx66lm1g45g. You might want 
to use this as reference.

[0] https://lore.kernel.org/all/20210812150135.4005-2-zhengxunli.mxic@gmail.com/

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.