RE: erasesize

RE: erasesize

[Frederic Giasson]

	... Maybe it should be passed through the arg pointer in the
ioctl(), in a 2 u_long sized structure?

Frédéric Giasson 




-----Original Message-----
From: Frederic Giasson [mailto:fgiasson@mediatrix.com]
Sent: Tuesday, June 05, 2001 8:49 AM
To: 'David Woodhouse'; Abraham vd Merwe
Cc: MTD for Linux
Subject: RE: erasesize 


	I have a question too about the erase->len ( erasesize ).  I have a
flash chip with variable block sizes, and I am using cfi_cmdset_0002.  Where
should that ->len be set?  When I printk the value held by erase->len just
before calling do_erase_oneblock() in cfi_amdstd_erase_varsize(), I get a
dummy value.  I suspect that it should be set according to the
mtd_erase_region_info structure, but it is not done. 

	Does anyone has a clue about it?  

Thanks!

Frédéric Giasson   






-----Original Message-----
From: David Woodhouse [mailto:dwmw2@infradead.org]
Sent: Tuesday, June 05, 2001 8:30 AM
To: Abraham vd Merwe
Cc: MTD for Linux
Subject: Re: erasesize 



abraham@2d3d.co.za said:
>  What should I set erasesize to when the flash chips have multiple
> erase sizes (and therefor I use eraseregions to get erasesize info)?
> Is 0 acceptable or should I set it to something else - it doesn't
> really make sense to put any value in this after all...

See the other Intel driver. Set the erase size to the 'major' erase size 
for the device, then fill in the appropriate structure to represent the 
other regions.

--
dwmw2



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Re: erasesize

[David Woodhouse]

fgiasson@mediatrix.com said:
> 	... Maybe it should be passed through the arg pointer in the ioctl(),
> in a 2 u_long sized structure?

I don't fully understand the question. The 'len' member of the struct 
erase_info contains the total length of the erase requested by the user of 
the MTD device. The only connexion with the device's erase size(s) is that 
obviously the range to be erase must start and end on an eraseblock 
boundary.

cfi_amdstd_erase_varsize() is an internal function intended to issue the
magic erase commands only to a certain address on the chip - it doesn't 
know anything about the erase size at that address, or care about the 
length field, does it?

--
dwmw2

RE: erasesize

[Frederic Giasson]

fgiasson@mediatrix.com said:
>  Therefore, this is why I think that the length of the block to erase
> whould be passed by the user. At least, this is what the code suggest.

That's correct. The user should pass the length of the region to erase.

For example, if you have a chip which has 8 * 8K regions, then 15 * 64K, 
the user may request that you erase 72K starting at offset 56K. That would 
require the magic incantation to be issued once at offset 56K to erase that 
8K block, and once at offset 64K to erase that 64K block.

--
dwmw2


We agree on that.  Now I am questionning on the portabilty of the piece of
code below
( which belongs to cfi_amdstd_erase_varsize() ) between different CFI ( and
maybe even non-cfi ) flashes.  
There is the reasons of my concern:


    if( instr->addr > mtd->size )
    {
        printk( "cfi_amdstd_erase_varsize: Requested erase region begining
out of range!\n" );
        printk( "instr->addr: %X, mtd->size: %d\n", instr->addr, mtd->size
);
		return -EINVAL;
    }

	if( ( instr->len + instr->addr ) > mtd->size )
    {
        printk( "cfi_amdstd_erase_varsize: Requested erase region end out of
range!\n" );
        printk( "instr->len: %X instr->addr: %X, mtd->size: %d\n",
instr->len, instr->addr, mtd->size );
        return -EINVAL;
    }


	/* Check that both start and end of the requested erase are
	 * aligned with the erasesize at the appropriate addresses.
	 */
	/* Skip all erase regions which are ended before the start of 
	   the requested erase. Actually, to save on the calculations,
	   we skip to the first erase region which starts after the
	   start of the requested erase, and then go back one.
	*/
	i = 0;
    while( ( i < mtd->numeraseregions ) && ( instr->addr >=
regions[i].offset ) )
    {
	       i++;
    }
	i--;

	/* OK, now i is pointing at the erase region in which this 
	   erase request starts. Check the start of the requested
	   erase range is aligned with the erase size which is in
	   effect here.
	*/
    if( instr->addr & ( regions[i].erasesize - 1 ) )
    {
        printk( "cfi_amdstd_erase_varsize: Erase region begin address as to
be aligned with physical sector.\n" );
		return -EINVAL;
    }


	/* Remember the erase region we start on */
	first = i;
	/* Next, check that the end of the requested erase is aligned
	 * with the erase region at that address.
	 */
	while( ( i < mtd->numeraseregions ) && ( (instr->addr + instr->len)
>= regions[i].offset ) )
    {
		i++;
    }
	/* As before, drop back one to point at the region in which
	   the address actually falls
	*/
	i--;

    if( (instr->addr + instr->len) & (regions[i].erasesize-1) )
    {
        printk( "cfi_amdstd_erase_varsize: End address is not aligned with
the region requested to be erased.\n" );
		return -EINVAL;
    }


        

Those 2 instructions ( from the code above)

    if( instr->addr & ( regions[i].erasesize - 1 ) )
	{
		[return error]
	}

and

    if( (instr->addr + instr->len) & (regions[i].erasesize-1) )
	{
		[return error]
	}

, which job are to ensure respectively that the start address of the block
to be erased is aligned
with the start of a physical sector, and that the instr->len is in a way so
that the block ends at
the very end of a physical sector, not a byte more or less.  

	With my flash ( Atmel, which is not CFI )  and probably most of the
existing flash memories on the market, 
it does the job.  However, it assumes 2 things:
	- sectors must have power-2 sizes 
	- sectors must be aligned on a multiple of their own size. 

	For example, a 32KB sector beggining at address 24KB wouldn't be OK.
I never seen a flash physically mapped in 
such a way, but maybe it is not always the case ( someone has the answer??
).

	
Whatever that answer would be, it would be safer to do as the code below
does:

    // Searching for a sector that begins at the starting address of the
block 
    // requested to be erased
    while( ( i < mtd->numeraseregions ) && ( instr->addr !=
regions[i].offset ) )
    {
		i++;
    }


	/* Remember the erase region we start on */
	first = i;

    // Searching for a sector that ends exactly at the last address of the
block 
    // requested to be erased
    while( 
            ( i < mtd->numeraseregions ) && 
            ( 
              ( instr->addr + instr->len ) != 
              ( regions[i].offset + regions[i].erasesize )
            )
         )
    {
	       i++;
    }
	
This would be safer, without taking longer to execute.
Anyone disagree?


Frédéric Giasson

RE: erasesize

[Frederic Giasson]

	I have a question too about the erase->len ( erasesize ).  I have a
flash chip with variable block sizes, and I am using cfi_cmdset_0002.  Where
should that ->len be set?  When I printk the value held by erase->len just
before calling do_erase_oneblock() in cfi_amdstd_erase_varsize(), I get a
dummy value.  I suspect that it should be set according to the
mtd_erase_region_info structure, but it is not done. 

	Does anyone has a clue about it?  

Thanks!

Frédéric Giasson   






-----Original Message-----
From: David Woodhouse [mailto:dwmw2@infradead.org]
Sent: Tuesday, June 05, 2001 8:30 AM
To: Abraham vd Merwe
Cc: MTD for Linux
Subject: Re: erasesize 



abraham@2d3d.co.za said:
>  What should I set erasesize to when the flash chips have multiple
> erase sizes (and therefor I use eraseregions to get erasesize info)?
> Is 0 acceptable or should I set it to something else - it doesn't
> really make sense to put any value in this after all...

See the other Intel driver. Set the erase size to the 'major' erase size 
for the device, then fill in the appropriate structure to represent the 
other regions.

--
dwmw2



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Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

erasesize

[Abraham vd Merwe]

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Hi!

What should I set erasesize to when the flash chips have multiple erase
sizes (and therefor I use eraseregions to get erasesize info)? Is 0
acceptable or should I set it to something else - it doesn't really make
sense to put any value in this after all...

-- 

Regards
 Abraham

Will Rogers never met you.

__________________________________________________________
 Abraham vd Merwe - 2d3D, Inc.

 Device Driver Development, Outsourcing, Embedded Systems

  Cell: +27 82 565 4451         Snailmail:
   Tel: +27 21 761 7549            Block C, Antree Park
   Fax: +27 21 761 7648            Doncaster Road
 Email: abraham@2d3d.co.za         Kenilworth, 7700
  Http: http://www.2d3d.com        South Africa


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Re: erasesize

[David Woodhouse]

abraham@2d3d.co.za said:
>  What should I set erasesize to when the flash chips have multiple
> erase sizes (and therefor I use eraseregions to get erasesize info)?
> Is 0 acceptable or should I set it to something else - it doesn't
> really make sense to put any value in this after all...

See the other Intel driver. Set the erase size to the 'major' erase size 
for the device, then fill in the appropriate structure to represent the 
other regions.

--
dwmw2