linux-kernel - Re: [PATCH 1/2] dt-bindings: mtd: spi-nor: Add reset-gpios property

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Date:   Tue, 30 Aug 2022 12:48:01 +0300
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Michael Walle <michael@...le.cc>
Cc:     Sai Krishna Potthuri <sai.krishna.potthuri@....com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Pratyush Yadav <pratyush@...nel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org, saikrishna12468@...il.com,
        git@....com
Subject: Re: [PATCH 1/2] dt-bindings: mtd: spi-nor: Add reset-gpios property

On 30/08/2022 12:36, Michael Walle wrote:
> Am 2022-08-30 11:21, schrieb Krzysztof Kozlowski:
>> On 29/08/2022 12:05, Sai Krishna Potthuri wrote:
>>> SPI-NOR flashes have RESET pin which can be toggled using GPIO
>>> controller, for those platforms reset-gpios property can be used to
>>> reset the flash device.
>>>
>>> Signed-off-by: Sai Krishna Potthuri <sai.krishna.potthuri@....com>
>>> ---
>>>  Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml 
>>> b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
>>> index 7149784a36ac..d2fc8e9c787f 100644
>>> --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
>>> +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
>>> @@ -70,6 +70,12 @@ properties:
>>>        be used on such systems, to denote the absence of a reliable 
>>> reset
>>>        mechanism.
>>>
>>> +  reset-gpios:
>>> +    description:
>>> +      contains a GPIO specifier.
>>
>> Skip this part - obvious.
>>
>>> The reset GPIO is asserted and then deasserted
>>> +      to perform device reset. If "broken-flash-reset" is present 
>>> then having
>>> +      this property does not make any difference.
>>
>> Isn't then broken-flash-reset conflicting with this one (e.g.
>> disallowing it)?
> 
> Sometimes the spi-nor driver needs to switch modes, which are persistent
> until you either switch em back or do a hardware reset (or software
> reset IIRC) of the flash. If broken-flash-reset is set, we try hard
> to leave the flash in the mode which it is normally in after reset or
> don't switch modes at all.
> Of course we cannot make sure, our shutdown gets called in each case,
> thus there is may be warning during startup.
> 
> So, even if you have a reset-gpio it might be broken I guess. Think
> of it being high active, but someone forgot the pull-up. So, if you
> do an unexpected reset, the flash chip might not be reset
> automatically. So yes, I think, even if there is a dedicated reset
> gpio, it could still be messed up. How likely is it? I don't know,
> probably not very.

OK, so let's keep it and allow both.

Best regards,
Krzysztof