Re: [PATCH 2/3] mtd: spi-nor: add 4bit block protection support

[Michael Walle <michael@walle.cc>]

Am 2020-03-17 12:35, schrieb Jungseung Lee:
> Hi, Micahel
> 
> On Tue, 2020-03-17 at 20:00 +0900, Jungseung Lee wrote:
>> Hi, Michael,
>> 
>> On Fri, 2020-03-13 at 17:24 +0100, Michael Walle wrote:
>> > Hi Jungseung,
>> >
>> > sorry for the late review.
>> >
>> 
>> Not at all. thanks for your review.
>> 
>> > Am 2020-03-04 12:07, schrieb Jungseung Lee:
>> > > Currently, we are supporting block protection only for
>> > > flash chips with 3 block protection bits in the SR register.
>> > > This patch enables block protection support for flashes with
>> > > 4 block protection bits(bp0-3).
>> > >
>> > > Signed-off-by: Jungseung Lee <js07.lee@samsung.com>
>> > > ---
>> > >  drivers/mtd/spi-nor/spi-nor.c | 82
>> > > ++++++++++++++++++++++++++++++++---
>> > >  include/linux/mtd/spi-nor.h   |  4 ++
>> > >  2 files changed, 79 insertions(+), 7 deletions(-)
>> > >
>> > > diff --git a/drivers/mtd/spi-nor/spi-nor.c
>> > > b/drivers/mtd/spi-nor/spi-nor.c
>> > > index c58c27552a74..31a2106e529a 100644
>> > > --- a/drivers/mtd/spi-nor/spi-nor.c
>> > > +++ b/drivers/mtd/spi-nor/spi-nor.c
>> > > @@ -238,6 +238,14 @@ struct flash_info {
>> > >  					 * status register. Must be
>> > > used with
>> > >  					 * SPI_NOR_HAS_TB.
>> > >  					 */
>> > > +#define SPI_NOR_4BIT_BP		BIT(17)	/*
>> > > +					 * Flash SR has 4 bit fields
>> > > (BP0-3)
>> > > +					 * for block protection.
>> > > +					 */
>> > > +#define SPI_NOR_BP3_SR_BIT6	BIT(18)	/*
>> > > +					 * BP3 is bit 6 of status
>> > > register.
>> > > +					 * Must be used with
>> > > SPI_NOR_4BIT_BP.
>> > > +					 */
>> > >
>> > >  	/* Part specific fixup hooks. */
>> > >  	const struct spi_nor_fixups *fixups;
>> > > @@ -1786,7 +1794,16 @@ static int spi_nor_erase(struct mtd_info
>> > > *mtd,
>> > > struct erase_info *instr)
>> > >
>> > >  static u8 spi_nor_get_bp_mask(struct spi_nor *nor)
>> > >  {
>> > > -	return SR_BP2 | SR_BP1 | SR_BP0;
>> > > +	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;
>> > > +
>> >
>> > can we just use the SR_BP3 eg:
>> >
>> > 	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;
>> > 	if (nor->flags & SNOR_F_HAS_4BIT_BP)
>> > 		mask |= SR_BP3;
>> > 	return mask;
>> >
>> >
>> 
>> I'd prefer this one too if we can, but there are some places to need
>> the real mask value. It is also used in other places such as
>> spi_nor_sr_lock/unlock.
>> 
>> > > +	if (nor->flags & SNOR_F_HAS_4BIT_BP) {
>> > > +		if (nor->flags & SNOR_F_HAS_SR_BP3_BIT6)
>> > > +			mask = mask | SR_BP3_BIT6;
>> > > +		else
>> > > +			mask = mask | SR_BP3_BIT5;
>> > > +	}
>> > > +
>> > > +	return mask;
>> > >  }
>> > >
>> > >  static u8 spi_nor_get_tb_mask(struct spi_nor *nor)
>> > > @@ -1797,12 +1814,26 @@ static u8 spi_nor_get_tb_mask(struct
>> > > spi_nor
>> > > *nor)
>> > >  		return SR_TB_BIT5;
>> > >  }
>> > >
>> > > +static u8 stm_get_bpval_from_sr(struct spi_nor *nor, u8 sr) {
>> > > +	u8 mask = spi_nor_get_bp_mask(nor);
>> > > +	u8 bp = sr & mask;
>> > > +
>> > > +	if (bp & SR_BP3_BIT6)
>> > > +		bp = (bp & ~BIT(6)) | BIT(5);
>> > > +
>> > > +	bp = bp >> SR_BP_SHIFT;
>> > > +
>> > > +	return bp;
>> > > +}
>> >
>> > Don't convert this. It makes the code really hard to read. See
>> > below.
>> >
>> > > +
>> > >  static int stm_get_min_prot_length(struct spi_nor *nor)
>> > >  {
>> > >  	int bp_slots, bp_slots_needed;
>> > > -	u8 mask = spi_nor_get_bp_mask(nor);
>> > >
>> > > -	bp_slots = (mask >> SR_BP_SHIFT) + 1;
>> >
>> > Then just keep this.
>> >
>> > > +	if (nor->flags & SNOR_F_HAS_4BIT_BP)
>> > > +		bp_slots = 1 << 4;
>> > > +	else
>> > > +		bp_slots = 1 << 3;
>> > >
>> > >  	/* Reserved one for "protect none" and one for "protect all".
>> > > */
>> > >  	bp_slots = bp_slots - 2;
>> > > @@ -1821,9 +1852,8 @@ static void stm_get_locked_range(struct
>> > > spi_nor
>> > > *nor, u8 sr, loff_t *ofs,
>> > >  {
>> > >  	struct mtd_info *mtd = &nor->mtd;
>> > >  	int min_prot_len;
>> > > -	u8 mask = spi_nor_get_bp_mask(nor);
>> > >  	u8 tb_mask = spi_nor_get_tb_mask(nor);
>> > > -	u8 bp = (sr & mask) >> SR_BP_SHIFT;
>> > > +	u8 bp = stm_get_bpval_from_sr(nor, sr);
>> >
>> > also this.
>> >
> 
> hmm, it looks like we still need some convertion here to get the exact
> bp value.

OK I see. What has confused me before was that some "fixups" were done
in helper functions whereas others where done in the actual
stm_lock/stm_unlock().

What do you think about:

(1) read the BP bits, if they are not consecutive move them around and
     normalize the value, eg. fix them up to be
         SR_BP3 | SR_BP2 | SR_BP1 | SR_BP0  >> SR_BP_SHIFT
(2) do the operations on these bits, eg this should not shift the
     value by SR_BP_SHIFT anymore. This would be done in (3)
(3) convert it back to the representation the flash would need it.

So there could be a function spi_nor_get_bp_val() for (1) and
spi_nor_set_bp_val() for (3).

u8 spi_nor_get_bp_val(u8 sr)
{
     u8 val;

     val = sr & (SR_BP2 | SR_BP1 | SR_BP0);

     if (nor->flags & SNOR_F_HAS_4BIT_BP)
         if (nor->flags & SNOR_F_HAS_SR_BP3_BIT6 && sr & SR_BP3_BIT6)
             val |= SR_BP3;
         else
             val |= sr & SR_BP3

     return val >> SR_BP_SHIFT;
}

void spi_nor_set_bp_val(u8 val, u8 *sr)
{
     u8 bp3_bit;

     val <<= SR_BP_SHIFT;

     /* clear and set common bits */
     *sr &= ~(SR_BP2 | SR_BP1 | SR_BP0);
     *sr |= val & (SR_BP2 | SR_BP1 | SR_BP0)

     /* BP3 is special because it may be on different bits */
     if (nor->flags & SNOR_F_HAS_4BIT_BP) {
         if (nor->flags & SNOR_F_HAS_SR_BP3_BIT6)
             bp3_bit = SR_BP3_BIT6;
         else
             bp3_bit = SR_BP3;

         if (val & SR_BP3)
             *sr |= bp3_bit;
         else
             *sr &= ~bp3_bit;
     }
}

This way we'd have all the fixups in one place.


-michael

>> > 	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;
>> > 	if (nor->flags & SNOR_F_HAS_4BIT_BP)
>> > 		mask |= SR_BP3;
>> > 	return mask;


}


-michael

> 
> Thanks,
> 
>> > >
>> > >  	if (!bp) {
>> > >  		/* No protection */
>> > > @@ -1881,7 +1911,7 @@ static int stm_is_unlocked_sr(struct
>> > > spi_nor
>> > > *nor, loff_t ofs, uint64_t len,
>> > >
>> > >  /*
>> > >   * Lock a region of the flash. Compatible with ST Micro and
>> > > similar
>> > > flash.
>> > > - * Supports the block protection bits BP{0,1,2} in the status
>> > > register
>> > > + * Supports the block protection bits BP{0,1,2}/BP{0,1,2,3} in
>> > > the
>> > > status register
>> > >   * (SR). Does not support these features found in newer SR
>> > > bitfields:
>> > >   *   - SEC: sector/block protect - only handle SEC=0 (block
>> > > protect)
>> > >   *   - CMP: complement protect - only support CMP=0 (range is
>> > > not
>> > > complemented)
>> > > @@ -1889,7 +1919,7 @@ static int stm_is_unlocked_sr(struct
>> > > spi_nor
>> > > *nor, loff_t ofs, uint64_t len,
>> > >   * Support for the following is provided conditionally for some
>> > > flash:
>> > >   *   - TB: top/bottom protect
>> > >   *
>> > > - * Sample table portion for 8MB flash (Winbond w25q64fw):
>> > > + * Sample table portion for 8MB flash (Winbond w25q64fw / BP0-
>> > > 2):
>> > >   *
>> > >   *   SEC  |  TB   |  BP2  |  BP1  |  BP0  |  Prot Length  |
>> > > Protected
>> > > Portion
>> > >   *
>> > > -----------------------------------------------------------------
>> > > ---------
>> > > @@ -1909,6 +1939,32 @@ static int stm_is_unlocked_sr(struct
>> > > spi_nor
>> > > *nor, loff_t ofs, uint64_t len,
>> > >   *    0   |   1   |   1   |   0   |   1   |  2 MB         |
>> > > Lower
>> > > 1/4
>> > >   *    0   |   1   |   1   |   1   |   0   |  4 MB         |
>> > > Lower
>> > > 1/2
>> > >   *
>> > > + * Sample table portion for 64MB flash (Micron n25q512ax3 / BP0-
>> > > 3):
>> > > + *
>> > > + *   TB   |  BP3  |  BP2  |  BP1  |  BP0  |  Prot Length  |
>> > > Protected
>> > > Portion
>> > > + *
>> > > -----------------------------------------------------------------
>> > > ---------
>> > > + *    0   |   0   |   0   |   0   |   0   |  NONE         | NONE
>> > > + *    0   |   0   |   0   |   0   |   1   |   64 KB       |
>> > > Upper
>> > > 1/1024
>> > > + *    0   |   0   |   0   |   1   |   0   |  128 KB       |
>> > > Upper
>> > > 1/512
>> > > + *    0   |   0   |   0   |   1   |   1   |  256 KB       |
>> > > Upper
>> > > 1/256
>> > > + *   ...
>> > > + *    0   |   1   |   0   |   0   |   1   |  16 MB        |
>> > > Upper
>> > > 1/4
>> > > + *    0   |   1   |   0   |   1   |   0   |  32 MB        |
>> > > Upper
>> > > 1/2
>> > > + *    0   |   1   |   0   |   1   |   1   |  64 MB        | ALL
>> > > + *    0   |   1   |   1   |   0   |   0   |  64 MB        | ALL
>> > > + *   ...
>> > > + *
>> > > ------|-------|-------|-------|-------|---------------|----------
>> > > ---------
>> > > + *    1   |   0   |   0   |   0   |   0   |   NONE        | NONE
>> > > + *    1   |   0   |   0   |   0   |   1   |   64 KB       |
>> > > Lower
>> > > 1/1024
>> > > + *    1   |   0   |   0   |   1   |   0   |  128 KB       |
>> > > Lower
>> > > 1/512
>> > > + *    1   |   0   |   0   |   1   |   1   |  256 KB       |
>> > > Lower
>> > > 1/256
>> > > + *   ...
>> > > + *    1   |   1   |   0   |   0   |   1   |  16 MB        |
>> > > Lower
>> > > 1/4
>> > > + *    1   |   1   |   0   |   1   |   0   |  32 MB        |
>> > > Lower
>> > > 1/2
>> > > + *    1   |   1   |   0   |   1   |   1   |  64 MB        | ALL
>> > > + *    1   |   1   |   1   |   0   |   0   |  64 MB        | ALL
>> > > + *   ...
>> > > + *
>> > >   * Returns negative on errors, 0 on success.
>> > >   */
>> > >  static int stm_lock(struct spi_nor *nor, loff_t ofs, uint64_t
>> > > len)
>> > > @@ -1960,6 +2016,9 @@ static int stm_lock(struct spi_nor *nor,
>> > > loff_t
>> > > ofs, uint64_t len)
>> > >  		min_prot_len = stm_get_min_prot_length(nor);
>> > >  		pow = ilog2(lock_len) - ilog2(min_prot_len) + 1;
>> > >  		val = pow << SR_BP_SHIFT;
>> > > +
>> > > +		if (val & BIT(5) && mask & SR_BP3_BIT6)
>> > > +			val = (val & ~BIT(5)) | BIT(6);
>> >
>> > .. and the use just the following here:
>> >
>> > if (nor->flags & SNOR_F_HAS_SR_BP3_BIT6 && val & SR_BP3)
>> > 	val = (val & ~SR_BP3) | SR_BP3_BIT6;
>> >
>> > Ie. just use the "normal case" where all BP bits are next to each
>> > other
>> > and then fixup the resulting value and shift the SR3 bit if
>> > necessary.
>> > This will be much easier to read.
>> >
>> 
>> Yes, I agree. It would be better to minimize this kind of conversion
>> in
>> one place.
>> 
>> > >  	}
>> > >
>> > >  	if (val & ~mask)
>> > > @@ -2042,6 +2101,9 @@ static int stm_unlock(struct spi_nor *nor,
>> > > loff_t ofs, uint64_t len)
>> > >  		pow = ilog2(lock_len) - ilog2(min_prot_len) + 1;
>> > >  		val = pow << SR_BP_SHIFT;
>> > >
>> > > +		if (val & BIT(5) && mask & SR_BP3_BIT6)
>> > > +			val = (val & ~BIT(5)) | BIT(6);
>> > > +
>> >
>> > here would be the other way around:
>> >
>> > if (nor->flags & SNOR_F_HAS_SR_BP3_BIT6 && val & SR_BP3_BIT6)
>> > 	val = (val & ~SR_BP3_BIT6) | SR_BP3;
>> >
>> >
>> > >  		/* Some power-of-two sizes are not supported */
>> > >  		if (val & ~mask)
>> > >  			return -EINVAL;
>> > > @@ -5244,6 +5306,12 @@ int spi_nor_scan(struct spi_nor *nor,
>> > > const
>> > > char
>> > > *name,
>> > >  	if (info->flags & USE_CLSR)
>> > >  		nor->flags |= SNOR_F_USE_CLSR;
>> > >
>> > > +	if (info->flags & SPI_NOR_4BIT_BP) {
>> > > +		nor->flags |= SNOR_F_HAS_4BIT_BP;
>> > > +		if (info->flags & SPI_NOR_BP3_SR_BIT6)
>> > > +			nor->flags |= SNOR_F_HAS_SR_BP3_BIT6;
>> > > +	}
>> > > +
>> > >  	if (info->flags & SPI_NOR_NO_ERASE)
>> > >  		mtd->flags |= MTD_NO_ERASE;
>> > >
>> > > diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-
>> > > nor.h
>> > > index de90724f62f1..0190ed21576a 100644
>> > > --- a/include/linux/mtd/spi-nor.h
>> > > +++ b/include/linux/mtd/spi-nor.h
>> > > @@ -129,7 +129,9 @@
>> > >  #define SR_BP1			BIT(3)	/* Block protect
>> > > 1
>> > > */
>> > >  #define SR_BP2			BIT(4)	/* Block protect
>> > > 2
>> > > */
>> > >  #define SR_TB_BIT5		BIT(5)	/* Top/Bottom
>> > > protect */
>> > > +#define SR_BP3_BIT5		BIT(5)	/* Block protect
>> > > 3
>> > > */
>> >
>> > IMHO just SR_BP3. but that is a matter of taste. But it is easier
>> > on
>> > the eye in the mask = SR_BP3 | SR_BP2 etc case.
>> >
>> 
>> SR_BP3 would be a more appropriate name if we could set the case with
>> all BP bits next to each other as the "normal case."
>> 
>> I'm going to write patches based on latest spi-nor/next including
>> what
>> you mentioned.
>> 
>> Thanks,
>> 
>> > -michael
>> >
>> > >  #define SR_TB_BIT6		BIT(6)	/* Top/Bottom
>> > > protect */
>> > > +#define SR_BP3_BIT6		BIT(6)	/* Block protect
>> > > 3
>> > > */
>> > >  #define SR_SRWD			BIT(7)	/* SR write
>> > > protect
>> > > */
>> > >  /* Spansion/Cypress specific status bits */
>> > >  #define SR_E_ERR		BIT(5)
>> > > @@ -240,6 +242,8 @@ enum spi_nor_option_flags {
>> > >  	SNOR_F_HAS_16BIT_SR	= BIT(9),
>> > >  	SNOR_F_NO_READ_CR	= BIT(10),
>> > >  	SNOR_F_HAS_SR_TB_BIT6	= BIT(11),
>> > > +	SNOR_F_HAS_4BIT_BP	= BIT(12),
>> > > +	SNOR_F_HAS_SR_BP3_BIT6	= BIT(13),
>> > >
>> > >  };
>> 
>> 

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