lkml.org 
[lkml]   [2018]   [Apr]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [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@brown.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@brown.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) */
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2018-04-20 23:28    [W:0.096 / U:3.468 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site