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Subject: Re: [PATCH 11/13] mtd: spinand: Add support for Power-on-Reset (PoR)
 instruction
To:     Miquel Raynal <miquel.raynal@bootlin.com>
CC:     Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Mark Brown <broonie@kernel.org>,
        Patrice Chotard <patrice.chotard@foss.st.com>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <linux-spi@vger.kernel.org>, Pratyush Yadav <p.yadav@ti.com>
References: <20210713130538.646-1-a-nandan@ti.com>
 <20210713130538.646-12-a-nandan@ti.com> <20210806210840.65c06b67@xps13>
 <403a2b26-fd95-31ab-8992-a6e6862249e6@ti.com> <20210820141822.03d658b8@xps13>
From:   Apurva Nandan <a-nandan@ti.com>
Message-ID: <c4a1eae9-7c0b-62c8-f10a-000e65c94f1b@ti.com>
Date:   Fri, 20 Aug 2021 19:11:58 +0530
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Hi Miquèl,

On 20/08/21 5:48 pm, Miquel Raynal wrote:
> Hi Apurva,
> 
> Apurva Nandan <a-nandan@ti.com> wrote on Fri, 20 Aug 2021 17:09:07
> +0530:
> 
>> Hi Miquèl,
>>
>> On 07/08/21 12:38 am, Miquel Raynal wrote:
>>> Hi Apurva,
>>>
>>> Apurva Nandan <a-nandan@ti.com> wrote on Tue, 13 Jul 2021 13:05:36
>>> +0000:
>>>    
>>>> Manufacturers like Gigadevice and Winbond are adding Power-on-Reset
>>>> functionality in their SPI NAND flash chips. PoR instruction consists
>>>> of a 66h command followed by 99h command, and is different from the FFh
>>>> reset. The reset command FFh just clears the status only registers,
>>>> while the PoR command erases all the configurations written to the
>>>> flash and is equivalent to a power-down -> power-up cycle.
>>>>
>>>> Add support for the Power-on-Reset command for any flash that provides
>>>> this feature.
>>>>
>>>> Datasheet: https://www.winbond.com/export/sites/winbond/datasheet/W35N01JW_Datasheet_Brief.pdf
>>>>
>>>> Signed-off-by: Apurva Nandan <a-nandan@ti.com>
>>>> ---
>>>
>>> [...]
>>> 				\
>>>> @@ -218,6 +230,8 @@ struct spinand_device;
>>>>     * reading/programming/erasing when the RESET occurs. Since we always
>>>>     * issue a RESET when the device is IDLE, 5us is selected for both initial
>>>>     * and poll delay.
>>>> + * Power on Reset can take max upto 500 us to complete, so sleep for 1000 us
>>>
>>> s/max upto/up to/
>>>    
>>
>> Okay!
>>
>>>> + * to 1200 us safely.
>>>
>>> I don't really get why, if the maximum is 500, then let's wait for
>>> 500us.
>>>    
>>
>> Generally we keep some margin from the maximum time, no?
> 
> Well, yes and no.
> 
> If you know that an operation will last Xms and have nothing else to
> do, then you can take some margin if you are in a probe (called once)
> but definitely not if you are in a fast path.
> 

I think as PoR reset would be called at every mtd_suspend() call, so we 
can reduce the delay. And we would be expecting some time gap before the 
next mtd_resume() call.

> Otherwise the best is to have some kind of signaling but I'm not sure
> you'll have one for the reset op...
> 

According to public datasheet, it doesn't set the busy bit during reset.

So do you suggest in the favor of removing the delay margin?

>>
>>>>     */
>>>>    #define SPINAND_READ_INITIAL_DELAY_US	6
>>>>    #define SPINAND_READ_POLL_DELAY_US	5
>>>> @@ -227,6 +241,8 @@ struct spinand_device;
>>>>    #define SPINAND_WRITE_POLL_DELAY_US	15
>>>>    #define SPINAND_ERASE_INITIAL_DELAY_US	250
>>>>    #define SPINAND_ERASE_POLL_DELAY_US	50
>>>> +#define SPINAND_POR_MIN_DELAY_US	1000
>>>> +#define SPINAND_POR_MAX_DELAY_US	1200
>>>>    >>   #define SPINAND_WAITRDY_TIMEOUT_MS	400
>>>>    >> @@ -351,6 +367,7 @@ struct spinand_ecc_info {
>>>>    #define SPINAND_HAS_QE_BIT		BIT(0)
>>>>    #define SPINAND_HAS_CR_FEAT_BIT		BIT(1)
>>>>    #define SPINAND_HAS_OCTAL_DTR_BIT	BIT(2)
>>>> +#define SPINAND_HAS_POR_CMD_BIT		BIT(3)
>>>>    >>   /**
>>>>     * struct spinand_ondie_ecc_conf - private SPI-NAND on-die ECC engine structure
>>>
>>>
>>>
>>>
>>> Thanks,
>>> Miquèl
>>>
>>> ______________________________________________________
>>> Linux MTD discussion mailing list
>>> http://lists.infradead.org/mailman/listinfo/linux-mtd/
>>>    
>>
>> Thanks,
>> Apurva Nandan
> 
> Thanks,
> Miquèl
> 

Thanks,
Apurva Nandan