linux-kernel - Re: [RFC] spi-nor: fix cross die reads on Micron multi-die devices

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Message-ID: <CAJorgdvD9WCsHCoRt05tn-vh_1oqsCZiMehbVKQtynocxX_-wQ@mail.gmail.com>
Date:	Wed, 20 Jan 2016 12:01:06 +0000
From:	Adam Somerville <adamsomerville@...il.com>
To:	Bean Huo 霍斌斌 (beanhuo) 
	<beanhuo@...ron.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"zajec5@...il.com" <zajec5@...il.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	"jteki@...nedev.com" <jteki@...nedev.com>,
	"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
	"furquan@...gle.com" <furquan@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] spi-nor: fix cross die reads on Micron multi-die devices

Hi,

Thanks for looking at the this.

I can rewrite so it only affects N25Q devices, I hoped a simpler
implementation would outweigh the small overhead incurred on non
affected devices.

Do you know if there are any plans for MT25* based multi-die devices
and if they would have the same issue?

Thanks,

Adam

On Wed, Jan 20, 2016 at 2:45 AM, Bean Huo 霍斌斌 (beanhuo)
<beanhuo@...ron.com> wrote:
> Hi, Adam
> This is true, but this only exist in Micron 65nm spi nor N25Q.
> For our 45nm spi nor MT25Q , MT25TL and MT25Q, does exist this question.
> So I think, can you differentiate between these in your patch?
>
>> From: Adam Somerville <adamsomerville@...il.com>
>>
>> So as far as I can see there is a bug in the spi-nor driver when issuing die
>> boundary crossing reads on Micron multi-die devices.
>> Micron N25Q512A, N25Q00AA and probably any other Micron multi-die
>> devices do not support a single read request that crosses a die boundary.
>>
>> The current behaviour is that the address on the device wraps back to the
>> start of the first die, with any data returned beyond the boundary being from
>> the start of the first die.
>>