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

[<Tudor.Ambarus@xxxxxxxxxxxxx>]

On Monday, March 23, 2020 8:27:13 PM EET Michael Walle wrote:
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> 
> 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.
 
> 
> > On a 16Mbit flash with 64KByte erase sector, the following changed
> > for the lock operation:
> > 
> > Number of blocks | BP2:0 before | BP2:0 now |
> > 
> >                1 | 010b         | 001b      |
> >                2 | 110b         | 010b      |
> >                3 | 110b         | 010b      |
> >                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.
> 
> I don't know if that is really what a user really want. Because you'd
> end up with regions which the user believes are locked but are not.

True. I'm thinking of how we can improve this, but it's not in the scope of 
this patch set, because the behavior is not changed.

> IMHO if you'd have to make a choice I'd prefer to have the remainder
> locked. Not the other way around. Esp. since the user explicitly
> express to have a region locked.
> 

We can still talk about this. Please notice that the formula that we want to 
introduce does the same thing as described in this commit message: for 
unaligned locks, it round down the length, and for unaligned unlocks it rounds 
up the length.

I'm waiting for a reply.
ta


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