linux-kernel - Re: [PATCH v2] mtd: spi-nor: clear Winbond Extended Address Reg on switch to 3-byte addressing.

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Date:   Sat, 21 Apr 2018 07:28:19 +1000
From:   NeilBrown <neil@...wn.name>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Marek Vasut <marek.vasut@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "Brian Norris" <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mtd: spi-nor: clear Winbond Extended Address Reg on switch to 3-byte addressing.

On Fri, Apr 20 2018, Boris Brezillon wrote:

> Hi Neil,
>
> On Mon, 16 Apr 2018 09:42:30 +1000
> NeilBrown <neil@...wn.name> wrote:
>
>> Winbond spi-nor flash 32MB and larger have an 'Extended Address
>> Register' as one option for addressing beyond 16MB (Macronix
>> has the same concept, Spansion has EXTADD bits in the Bank Address
>> Register).
>> 
>> According to section
>>    8.2.7 Write Extended Address Register (C5h)
>> 
>> of the Winbond W25Q256FV data sheet (256M-BIT SPI flash)
>> 
>>    The Extended Address Register is only effective when the device is
>>    in the 3-Byte Address Mode.  When the device operates in the 4-Byte
>>    Address Mode (ADS=1), any command with address input of A31-A24
>>    will replace the Extended Address Register values. It is
>>    recommended to check and update the Extended Address Register if
>>    necessary when the device is switched from 4-Byte to 3-Byte Address
>>    Mode.
>> 
>> So the documentation suggests clearing the EAR after switching to
>> 3-byte mode.  Experimentation shows that the EAR is *always* one after
>> the switch to 3-byte mode, so clearing the EAR is mandatory at
>> shutdown for a subsequent 3-byte-addressed reboot to work.
>> 
>> Note that some SOCs (e.g. MT7621) do not assert a reset line at normal
>> reboot, so we cannot rely on hardware reset.  The MT7621 does assert a
>> reset line at watchdog-reset.
>> 
>> Signed-off-by: NeilBrown <neil@...wn.name>
>
> We should probably backport the fix. Can you add a Fixes and Cc-stable
> tag?

It's a bit weird having Fixes when this isn't a regression, but I guess
it doesn't hurt.
I chose
  Fixes: 59b356ffd0b0 ("mtd: m25p80: restore the status of SPI flash when exiting")
as this patch it useless without that one.

I also fixed the comment and have resent.

Thanks,
NeilBrown

>
>> ---
>> 
>> following a helpful discussion with Marek, I've revised the description
>> a little, and make the code change specific to winbond.
>> I've change the OP names to RDEAR and WREAR instead of RDXA and WRXA to
>> match names used in the Macronix documentation.  Winbond documentation
>> doesn't provide abbreviated OP names.
>> 
>> Thanks,
>> NeilBrown
>> 
>> 
>>  drivers/mtd/spi-nor/spi-nor.c | 13 +++++++++++++
>>  include/linux/mtd/spi-nor.h   |  2 ++
>>  2 files changed, 15 insertions(+)
>> 
>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>> index d445a4d3b770..0d0af0acf8b9 100644
>> --- a/drivers/mtd/spi-nor/spi-nor.c
>> +++ b/drivers/mtd/spi-nor/spi-nor.c
>> @@ -284,6 +284,19 @@ static inline int set_4byte(struct spi_nor *nor, const struct flash_info *info,
>>  		if (need_wren)
>>  			write_disable(nor);
>>  
>> +		if (!status && !enable &&
>> +		    JEDEC_MFR(info) == SNOR_MFR_WINBOND) {
>> +			/* On Winbond W25Q256FV, leaving 4byte mode causes
>
> We use regular kernel-comment style in MTD:
>
> 			/*
> 			 * blablabla
> 			 */
>
> Thanks,
>
> Boris
>
>> +			 * the Extended Address Register to be set to 1, so all
>> +			 * 3-byte-address reads come from the second 16M.
>> +			 * We must clear the register to enable normal behavior.
>> +			 */
>> +			write_enable(nor);
>> +			nor->cmd_buf[0] = 0;
>> +			nor->write_reg(nor, SPINOR_OP_WREAR, nor->cmd_buf, 1);
>> +			write_disable(nor);
>> +		}
>> +
>>  		return status;
>>  	default:
>>  		/* Spansion style */
>> diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
>> index de36969eb359..e60da0d34cc1 100644
>> --- a/include/linux/mtd/spi-nor.h
>> +++ b/include/linux/mtd/spi-nor.h
>> @@ -62,6 +62,8 @@
>>  #define SPINOR_OP_RDCR		0x35	/* Read configuration register */
>>  #define SPINOR_OP_RDFSR		0x70	/* Read flag status register */
>>  #define SPINOR_OP_CLFSR		0x50	/* Clear flag status register */
>> +#define SPINOR_OP_RDEAR		0xc8	/* Read Extended Address Register */
>> +#define SPINOR_OP_WREAR		0xc5	/* Write Extended Address Register */
>>  
>>  /* 4-byte address opcodes - used on Spansion and some Macronix flashes. */
>>  #define SPINOR_OP_READ_4B	0x13	/* Read data bytes (low frequency) */

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