From: Pratyush Yadav <p.yadav@ti.com>
To: <zhengxunli@mxic.com.tw>
Cc: <broonie@kernel.org>, <jaimeliao@mxic.com.tw>,
<linux-mtd@lists.infradead.org>, <linux-spi@vger.kernel.org>,
<miquel.raynal@bootlin.com>, <tudor.ambarus@microchip.com>
Subject: Re: [PATCH v3 1/3] mtd: spi-nor: macronix: add support for Macronix octal dtr operation
Date: Tue, 4 May 2021 13:12:20 +0530 [thread overview]
Message-ID: <20210504074218.s2zezkt3imaanfmr@ti.com> (raw)
In-Reply-To: <OF2365AB9C.87E8927D-ON482586CA.0029B8EB-482586CB.001E5C1A@mxic.com.tw>
On 04/05/21 01:31PM, zhengxunli@mxic.com.tw wrote:
> Hi Pratyush,
>
> Thanks for your comment on this patch.
>
> "Pratyush Yadav" <p.yadav@ti.com> wrote on 2021/04/27 上午 10:36:06:
>
[...]
> > > + if (!enable)
> > > + spi_nor_spimem_setup_op(nor, &op, SNOR_PROTO_8_8_8_DTR);
> >
> > When disabling, the op would be in 8D-8D-8D mode so having a data length
>
> > of 1 would be invalid. This is currently the case even in the patches
> > that I sent for Micron and Cypress.
> >
> > I am not sure what the correct fix for this is though. One option is to
> > send the same byte twice, but I remember that on the Cypress flash the
> > second byte over-writes the register at the next address. I'm not sure
> > how Macronix flashes handle the second byte. Can you check what the
> > behavior for your flash is when you write 2 bytes to the register?
>
> I checked the behavior of Macronix and the second byte will overwrites the
> register.
Yes, I see the same behaviour on Micron and Cypress flashes. Can your
controller send a 1-byte write in 8D mode? I am curious if this is
possible and how flashes react to it.
My theory is that even if you ask the controller to send 1 byte in 8D
mode, it won't deassert the CS till the end of the cycle. This would
result the flash in taking the default value of the lines as the second
byte.
> Do we need to send the same bytes to resolve this error?
I think this is a design oversight by flash manufacturers. Having two
registers at consecutive addresses is problematic in 8D-8D-8D mode. The
only solution I see is to read the register at the next address, and set
its value as the second byte in the transaction. This way its value will
stay the same at the end of the transaction.
PS: If possible, please try to relay this issue to your hardware design
team. Hopefully they can come up with a clever solution for future
devices and make our lives easier ;-)
--
Regards,
Pratyush Yadav
Texas Instruments Inc.
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next prev parent reply other threads:[~2021-05-04 7:43 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 6:29 [PATCH v3 0/3] Add octal DTR support for Macronix flash Zhengxun Li
2021-04-20 6:29 ` [PATCH v3 1/3] mtd: spi-nor: macronix: add support for Macronix octal dtr operation Zhengxun Li
2021-04-27 2:36 ` Pratyush Yadav
2021-05-04 5:31 ` zhengxunli
2021-05-04 7:42 ` Pratyush Yadav [this message]
2021-05-05 8:29 ` zhengxunli
2021-04-20 6:29 ` [PATCH v3 2/3] mtd: spi-nor: macronix: add support for Macronix octaflash series Zhengxun Li
2021-04-27 2:47 ` Pratyush Yadav
2021-05-04 5:38 ` zhengxunli
2021-04-20 6:29 ` [PATCH v3 3/3] spi: mxic: patch for octal DTR mode support Zhengxun Li
2021-04-26 16:53 ` Mark Brown
2021-04-27 1:48 ` zhengxunli
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