Re: [PATCH v3 1/5] mtd: spi-nor: Fix gap in SR block protection locking

[<Tudor.Ambarus@xxxxxxxxxxxxx>]

On Monday, March 23, 2020 9:54:38 PM EET Michael Walle wrote:
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> Am 2020-03-23 20:20, schrieb Tudor.Ambarus@xxxxxxxxxxxxx:
> > On Monday, March 23, 2020 8:27:13 PM EET Michael Walle wrote:
> >> EXTERNAL EMAIL: Do not click links or open attachments unless you know
> >> the
> >> content is safe
> >> 
> >> Hi,
> >> 
> >> Am 2020-03-23 10:24, schrieb Tudor.Ambarus@xxxxxxxxxxxxx:
> >> > From: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
> >> > 
> >> > Fix the gap for the SR block protection, the BP bits were set with
> >> > a +1 value than actually needed. This patch does not change the
> >> > behavior of the locking operations, just fixes the protected areas.
> >> 
> >> So instead of rounding up, it does round down now?
> > 
> > No. Why do you say that it rounds up? The behavior is not changed, the
> > patch
> > merely fix the protected area, which was wrong before. The round down
> > is
> > present before this patch.
> 
> TBH I don't understand what this patch should do. Could you give an
> example?

sure, let me try to be more explicit.

> 
> >> > On a 16Mbit flash with 64KByte erase sector, the following changed
> 
> >> > for the lock operation:
> 16MBit is a bad example, because it is broken anyway, isn't it? We use a

it's not.

> 32Mbit flash where 2MB are locked and the second 2MB are unlocked. Eg. a
> 50/50 split. I haven't seen any issued. Shouldn't it be then completely
> locked according this the following example?

I don't follow.

The table from below was generated for the S25FL116K 16 Mbit flash. BTW, one 
has to disable CONFIG_MTD_SPI_NOR_USE_4K_SECTORS in order to test the locking. 
When you have a 4k sector erase, the locking is simply wrong, but this is 
another topic.

> 
> >> > Number of blocks | BP2:0 before | BP2:0 now |
> >> > 
> >> >                1 | 010b         | 001b      |

- number of blocks is how many blocks you want to lock. One would do for one 
block:
    flash_lock /dev/mtd 0 1
i.e. lock a single erase block starting from offset 0.

- "BP0:2 before" is the result of the operation "flash_lock /dev/mtd 0 1" 
before this patch

- "BP0:2 now" is the result of the operation "flash_lock /dev/mtd 0 1" using 
this patch

So before this patch, the lock operation was bad, because it locked 2 blocks 
instead of one.

> >> >                2 | 110b         | 010b      |

- lock 2 erase blocks starting from offset 0. Results before this patch, and 
after this patch. Continue the logic on the following lines.

oops there's a typo in column 2, sorry. The value in column 2 should have been 
011b.

So before this patch, when one requested to lock 2 block starting from offset 
0, we would obtain 4 blocks locked, and he should have obtained just 2.

The scope of this patch is to first fix the locking ops, so that we can 
introduce a more generic formula that gives the same results as before 
introducing it. Without this patch, the new formula will silently fix the bug 
that is described here.

> >> >                3 | 110b         | 010b      |
		^ typo s/110b/011b

rest of the examples are good.

Cheers,
ta

> >> >                4 | 100b         | 011b      |
> >> >                5 | 100b         | 011b      |
> >> >                6 | 100b         | 011b      |
> >> >                7 | 100b         | 011b      |
> >> >                8 | 101b         | 100b      |
> >> >                9 | 101b         | 100b      |
> >> >              
> >> >              ... | ...          | ...       |
> >> > 
> >> > For the lock operation, if one requests to lock an area that is not
> >> > matching the upper boundary of a BP protected area, we round down
> >> > the total length and lock less than the user requested, in order to
> >> > not lock more than the user actually requested.



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