linux-kernel - Re: [PATCH 1/2] mtd: spi-nor: add an option to force 3byte adressing mode

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Date:   Tue, 29 Aug 2017 09:40:06 +0200
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Marek Vasut <marek.vasut@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Mark Brown <broonie@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Gregory Clément 
        <gregory.clement@...e-electrons.com>, nadavh@...vell.com,
        Neta Zur Hershkovits <neta@...vell.com>,
        Omri Itach <omrii@...vell.com>,
        Hanna Hawa <hannah@...vell.com>,
        "jaz@...ihalf.com" <jaz@...ihalf.com>,
        Tomasz Nowicki <tn@...ihalf.com>
Subject: Re: [PATCH 1/2] mtd: spi-nor: add an option to force 3byte adressing mode

Hi Marek,

2017-08-29 1:24 GMT+02:00 Marek Vasut <marek.vasut@...il.com>:
> On 08/28/2017 11:14 PM, Marcin Wojtas wrote:
>> Hitherto code set 4B addressing mode for all SPI flashes whose
>> size exceeds 16MB. However, changing the default 3B access
>> in some cases may be harmful - it may happen that the Boot ROM
>> is not capable of handling non-default state of the SPI NOR
>> (e.g. after soft reset).
>
> No, this happens when your hardware is broken and does NOT reset the
> flash while reseting the CPU as well. If the flash is in some funny
> state (ie. middle of page program or erase cycle, which takes long OR
> 4byte addressing mode) and the CPU resets , then if the SPI NOR is not
> reset, your system will still get stuck . You need to fix your hardware
> such that you use the reset output of your CPU to detect when the CPU
> restarted and add logic to reset your storage as well.
>
> This stuff below is a poor workaround and has it's known problems which
> can only be solved by fixing the hardware. This problem keeps coming up
> repeatedly, just skim through the Linux MTD and U-Boot lists for other
> victims of bad HW design. I don't think I want to see it in the kernel
> as that would motivate people to use it rather than fixing their HW .
>

Understood. I just only got impression that attempts to overcome the
HW design faults in terms of keeping SPI NOR default state during boot
can be added - introducing SPI_NOR_4B_OPCODES seems to have no other
reason, however it favors only a group of devices that support it.

Best regards,
Marcin