Re: VIRTIO iface in mtd

From: "Marcin Krzemiński" <mar.krzeminski@gmail.com>
To: Boris Brezillon <bbrezillon@kernel.org>,
	Richard Weinberger <richard@nod.at>,
	Miquel Raynal <miquel.raynal@bootlin.com>
Cc: linux-mtd@lists.infradead.org
Subject: Re: VIRTIO iface in mtd
Date: Fri, 18 Jan 2019 21:03:17 +0100	[thread overview]
Message-ID: <f53fe2ac-c1a1-1e64-1f4c-046b8e9daa2b@gmail.com> (raw)
In-Reply-To: <20190117214654.08542c12@bbrezillon>

On 17.01.2019 21:46, Boris Brezillon wrote:
> +Richard and Miquel
>
> Hi Marcin,
>
> On Thu, 17 Jan 2019 21:16:19 +0100
> Marcin Krzemiński <mar.krzeminski@gmail.com> wrote:
>
>> Hello,
>>
>> recently I have spoken with Boris regarding new MTD driver
>> that will use VIRTIO interface to communicate with Qemu.
>> To specify how should this look like exactly I am bringing the topic
>> on ML.
> Thanks for starting this discussion.
Np :)
>
>> My understanding is that this driver will use VIRTIO to communicate
>> with Qemu. From Qemu side at the end there will be a file that will
>> simulate NAND/NOR. Is it correct?
> That's my understanding, but I'm not really a virtio or qemu expert so
> I might be wrong.
>
>> What use cases do you have in mind for this?
> I have one in mind: simulate NAND (in particular MLC NAND) behavior in
> a pseudo-realistic way to validate UBI/UBIFS code (or any other
> FS/wear-leveling/FTL code) we might want to use on top of such devices
In this place my question is what we remove from emulation?
I understand that communication layer is removed, however communication 
protocol
need t o stay? Eg. because NAND and OOB.

>
> I'd also like to replace nandsim by this emulation approach. Indeed,
> nandsim is emulating the parallel NAND protocol more than anything
> else, which we don't really care about unless we need to test the raw
> NAND framework (and I think there are better solutions to do that). On
> the other hand, because nandsim tries to use the full raw NAND stack,
> it's often hard to emulate real devices (ID-based detection does not
> work for ONFI/JEDEC compatible devices). All of this makes nandsim a
> poor choice when the user wants to emulate a NAND device to do
> post-mortem analysis using a NAND dump.
This I need to understand better. If we eg. have NAND dump, do we care 
with OOB or ECC,
or not?

At the end I also need to add, that I understand NOR devices, but 
unfortunately
I have low experience with NANDs. This could lead to some misunderstands :(

Thanks,
Marcin
>
> Richard probably a few more use cases ;-).
>
> Regards,
>
> Boris

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