Re: [PATCH] spi-nor: Verify written data in paranoid mode

From: Richard Weinberger <richard@nod.at>
To: "Csókás Bence" <csokas.bence@prolan.hu>
Cc: "Michael Walle" <mwalle@kernel.org>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	"Szentendrei, Tamás" <szentendrei.tamas@prolan.hu>,
	"Tudor Ambarus" <tudor.ambarus@linaro.org>,
	pratyush <pratyush@kernel.org>,
	"Miquel Raynal" <miquel.raynal@bootlin.com>,
	"Vignesh Raghavendra" <vigneshr@ti.com>
Subject: Re: [PATCH] spi-nor: Verify written data in paranoid mode
Date: Wed, 16 Apr 2025 15:09:03 +0200 (CEST)	[thread overview]
Message-ID: <373620122.295980015.1744808943985.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <dd3c7cc0-a568-4046-b105-e6786b5c80f8@prolan.hu>

----- Ursprüngliche Mail -----
> Von: "Csókás Bence" <csokas.bence@prolan.hu>
>>> Add MTD_SPI_NOR_PARANOID config option for verifying all written data to
>>> prevent silent bit errors to be undetected, at the cost of halving SPI
>>> bandwidth.
>> 
>> What is the use case for this? Why is it specific to SPI-NOR
>> flashes? Or should it rather be an MTD "feature". I'm not sure
>> whether this is the right way to do it, thus I'd love to hear more
>> about the background story to this.
> 
> Well, our case is quite specific, but we wanted to provide a general
> solution for upstream. In our case we have a component in the data path
> that can cause a burst bit error, on average after about a hundred
> megabytes written.

Hmm. So, there is a serve hardware issue you're working around.

> We _could_ make it MTD-wide, in our case we only have a NOR Flash
> onboard so this is where we added it. If it were in the MTD core, where
> would it make sense?

I'm not so sure whether it makes sense at all.
In it's current form, there is no recovery. So anything non-trivial
on top of the MTD will just see an -EIO and has to give up.
E.g. a filesystem will remount read-only.

Thanks,
//richard

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