linux-kernel - Re: [PATCH 3/3] MTD: spi-nor: add flag to not use sector erase.

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Date:	Fri, 1 May 2015 16:20:05 +0200
From:	Marek Vasut <marex@...x.de>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	"Rafa?? Mi??ecki" <zajec5@...il.com>,
	Alison Chaiken <alison_chaiken@...tor.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	"Bean Huo (beanhuo)" <beanhuo@...ron.com>,
	"grmoore@...era.com" <grmoore@...era.com>,
	linux-mtd@...ts.infradead.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] MTD: spi-nor: add flag to not use sector erase.

On Friday, May 01, 2015 at 09:05:15 AM, Michal Suchanek wrote:
> On 1 May 2015 at 01:13, Marek Vasut <marex@...x.de> wrote:
> > On Thursday, April 30, 2015 at 11:13:12 PM, Michal Suchanek wrote:
> >> The sector size of the flash memory is unclear from datasheet or may
> >> possibly vary between chips so add a flag to always use 4k blocks.
> >> 
> >> Currently 4k blocks are always used when possible but in the future
> >> somebody might want to do some optimizations with sector erase.
> >> 
> >> Signed-off-by: Michal Suchanek <hramrach@...il.com>
> > 
> > I _think_ you might be able to determine the size, no ?
> > 
> > One way is to ask the vendor, but you can also try something like:
> > 1) erase the whole SPI NOR
> > 2) overwrite it with zeroes (or ones ? I think it should be all ones
> > after erasing).
> > 3) Erase sector 0
> > 4) Read some 128 KiB back
> > 5) Observe what is the difference.
> 
> I can determine it for this particular chip. However, when the vendor
> datasheet says the block is 64/32K it might mean that chips with this
> ID can have either block size.

http://www.chingistek.com/img/Product_Files/Pm25LD010020datasheet%20v04.pdf
page 21:

SECTOR_ER (20h) erases 4kByte sector.
BLOCK_ER (d8h) erases 64kByte sector.

http://www.gigadevice.com/product/download/366.html?locale=en_US
page 27-28:

Sector Erase (SE) (20h) erases 4kByte sector
64KB Block Erase (BE) (d8h) erases 64kByte sector

> It's a value that we don't use anyway so I just mark it as unknown
> here for future reference.

Looks like standard SPI NOR opcodes [1], nothing unknown there ;-)

[1] include/linux/mtd/spi-nor.h

Best regards,
Marek Vasut
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