linux-kernel - Re: [PATCH v2 7/7] mtd: spi-nor: Rework the disabling of block write protection

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Message-ID: <20190825152231.165de3d7@collabora.com>
Date:   Sun, 25 Aug 2019 15:22:31 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     <Tudor.Ambarus@...rochip.com>
Cc:     <marek.vasut@...il.com>, <vigneshr@...com>,
        <miquel.raynal@...tlin.com>, <richard@....at>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 7/7] mtd: spi-nor: Rework the disabling of block
 write protection

On Sun, 25 Aug 2019 12:57:35 +0000
<Tudor.Ambarus@...rochip.com> wrote:

> On 08/25/2019 03:24 PM, Boris Brezillon wrote:
> > On Sat, 24 Aug 2019 12:00:48 +0000
> > <Tudor.Ambarus@...rochip.com> wrote:
> >   
> >> From: Tudor Ambarus <tudor.ambarus@...rochip.com>
> >>
> >> Get rid of MFR handling and implement specific manufacturer
> >> default_init() fixup hooks.
> >>
> >> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> >> ---
> >>  drivers/mtd/spi-nor/spi-nor.c | 30 ++++++++++++++++++++----------
> >>  1 file changed, 20 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> >> index fc9e14777212..f4e9fcca619f 100644
> >> --- a/drivers/mtd/spi-nor/spi-nor.c
> >> +++ b/drivers/mtd/spi-nor/spi-nor.c
> >> @@ -4146,6 +4146,16 @@ static int spi_nor_parse_sfdp(struct spi_nor *nor,
> >>  	return err;
> >>  }
> >>  
> >> +static void atmel_set_default_init(struct spi_nor *nor)
> >> +{
> >> +	nor->params.disable_block_protection = spi_nor_clear_sr_bp;
> >> +}
> >> +
> >> +static void intel_set_default_init(struct spi_nor *nor)
> >> +{
> >> +	nor->params.disable_block_protection = spi_nor_clear_sr_bp;  
> > 
> > That's weird: you can unlock blocks but locking is not
> > explicitly flagged as supported (SNOR_F_HAS_LOCK is not set). Is that
> > expected?  
> 
> Yes. Manufacturers have different methods for locking/unlocking blocks of
> memory. Right now we support just the stm/sr locking operations. sst26vf064b for
> example, uses dedicated registers for reading/writing which blocks are
> protected, and not the Status Register.
> 
> The reason for having disable_block_protection(), is that some spi-nor flashes
> are write protected by default after a power-on reset cycle, in order to avoid
> inadvertent writes during power-up. Backward compatibility imposes to disable
> the write block protection at power-up by default, so that you can erase/write
> the memory without having to send an unlock-all command. Which is bad in my
> opinion and that's why I proposed https://patchwork.ozlabs.org/patch/1133278/.
> 
> Even if sst26vf064b does not yet have the lock ops implemented (SNOR_F_HAS_LOCK
> is not set), I would like to be able to interact with it, so to disable the
> block protection at power-up. This flash, and others, support a Global Unlock
> Command which unlocks the entire memory array in a single cycle. We can't
> determine who supports this command purely by manufacturer type, and it's not
> discoverable through SFDP, so we'll have to add a nor->info flag for it:
> UNLOCK_GLOBAL_BLOCK (see https://patchwork.ozlabs.org/patch/1152606/).
> 
> In conclusion, even if SNOR_F_HAS_LOCK is not set (the locking ops are not
> implemented), we can still have disable_block_protection() mechanisms to unlock
> the entire flash at power-up.

Hm, okay, but what about those atmel/intel chips that support
SR_BP-based global unlock? Shouldn't they also support SR_BP-based
locking/unlocking?

> 
> >   
> >> +}
> >> +
> >>  static void macronix_set_default_init(struct spi_nor *nor)
> >>  {
> >>  	nor->params.quad_enable = macronix_quad_enable;
> >> @@ -4173,6 +4183,14 @@ static void spi_nor_manufacturer_init_params(struct spi_nor *nor)
> >>  {
> >>  	/* Init flash parameters based on MFR */
> >>  	switch (JEDEC_MFR(nor->info)) {
> >> +	case SNOR_MFR_ATMEL:
> >> +		atmel_set_default_init(nor);
> >> +		break;
> >> +
> >> +	case SNOR_MFR_INTEL:
> >> +		intel_set_default_init(nor);
> >> +		break;
> >> +
> >>  	case SNOR_MFR_MACRONIX:
> >>  		macronix_set_default_init(nor);
> >>  		break;
> >> @@ -4760,18 +4778,10 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
> >>  	if (info->flags & SPI_S3AN)
> >>  		nor->flags |=  SNOR_F_READY_XSR_RDY;
> >>  
> >> -	if (info->flags & SPI_NOR_HAS_LOCK)
> >> +	if (info->flags & SPI_NOR_HAS_LOCK) {  
> > 
> > If this flag implies SR_BP-based locking we should really rename it into
> > SPI_NOR_HAS_SR_BP_LOCK to avoid any confusion.  
> 
> Not only SR-based locking, should be a general flag that indicates that locking
> ops are supported whichever they are. I would keep the SPI_NOR_HAS_LOCK and let
> the manufacturer set its locking ops using the ->default_init() hook.

Okay, sounds good as long as the locking scheme is selected on a
per-manufacturer basis, not a per-chip basis.

> 
> >   
> >>  		nor->flags |= SNOR_F_HAS_LOCK;
> >> -
> >> -	/*
> >> -	 * Atmel, SST, Intel/Numonyx, and others serial NOR tend to power up
> >> -	 * with the software protection bits set.
> >> -	 */
> >> -	if (JEDEC_MFR(nor->info) == SNOR_MFR_ATMEL ||
> >> -	    JEDEC_MFR(nor->info) == SNOR_MFR_INTEL ||
> >> -	    JEDEC_MFR(nor->info) == SNOR_MFR_SST ||
> >> -	    nor->info->flags & SPI_NOR_HAS_LOCK)
> >>  		nor->params.disable_block_protection = spi_nor_clear_sr_bp;
> >> +	}
> >>  
> >>  	/* Init flash parameters based on flash_info struct and SFDP */
> >>  	spi_nor_init_params(nor);  
> > 
> >