Re: [PATCH 1/2] mtd: spi-nor: winbond: Add support for w25q01jv

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Pratyush Yadav <pratyush@kernel.org>
Cc: Tudor Ambarus <tudor.ambarus@linaro.org>,
	 Michael Walle <mwalle@kernel.org>,
	 Richard Weinberger <richard@nod.at>,
	 Vignesh Raghavendra <vigneshr@ti.com>,
	 Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	 Steam Lin <STLin2@winbond.com>,
	linux-mtd@lists.infradead.org,  linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mtd: spi-nor: winbond: Add support for w25q01jv
Date: Wed, 15 Jan 2025 20:10:39 +0100	[thread overview]
Message-ID: <87zfjrlwpc.fsf@bootlin.com> (raw)
In-Reply-To: <mafs08qrc5g44.fsf@kernel.org> (Pratyush Yadav's message of "Wed, 15 Jan 2025 14:03:23 +0000")

Hello Pratyush,

> Okay, I am confused because you said earlier that:
>
>> The bug that has been experienced followed this sequence:
>> - send the write enable command (non-volatile)
>> - wait for the ready/busy bit, ie. wait for the WEL bit to be set
>>   because it is non-volatile write
>> - active die is ready, (but idle die is not!)
>> - enter 4-byte address mode, only the die that is ready processes the
>>   command.
>
> Which says the WEL bit being set itself is racy. What I understand from
> that is one die is ready to take writes and the other is not. Now when
> you try to write the SR to enable 4B mode, it would only work on the die
> that got the WEL set. The other one ignores it and stays in 3B mode. Do
> I understand this correctly? To fix this you need to wait after the
> write enable, before you initiate the write SR operation.

Actually I think you're right. The thing is, Winbond WEL bit are
non-volatile by default, whereas you were assuming it would be. Maybe
the proper fix is to do both?
- Using the volatile 'write enable'
and
- Making sure we wait after the (other) commands tampering with all dies.

Thanks,
Miquèl

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