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Date:   Fri, 20 Aug 2021 16:17:44 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Apurva Nandan <a-nandan@ti.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>
Subject: Re: [PATCH 11/13] mtd: spinand: Add support for Power-on-Reset
 (PoR) instruction
Message-ID: <20210820161744.148b3003@xps13>
In-Reply-To: <c4a1eae9-7c0b-62c8-f10a-000e65c94f1b@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>
        <c4a1eae9-7c0b-62c8-f10a-000e65c94f1b@ti.com>
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Hi Apurva,

Apurva Nandan <a-nandan@ti.com> wrote on Fri, 20 Aug 2021 19:11:58
+0530:

> 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?

Well, it's microseconds, maybe you can reduce it a little bit but that
will be ok.

> 
> >>  
> >>>>     */
> >>>>    #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

Thanks,
Miquèl