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

From: Michal Suchanek <hramrach@gmail.com>
To: Marek Vasut <marex@denx.de>
Cc: David Woodhouse <dwmw2@infradead.org>,
	Brian Norris <computersforpeace@gmail.com>,
	"Rafa?? Mi??ecki" <zajec5@gmail.com>,
	Alison Chaiken <alison_chaiken@mentor.com>,
	Ben Hutchings <ben@decadent.org.uk>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	"Bean Huo (beanhuo)" <beanhuo@micron.com>,
	"grmoore@altera.com" <grmoore@altera.com>,
	linux-mtd@lists.infradead.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] MTD: spi-nor: add flag to not use sector erase.
Date: Fri, 1 May 2015 09:05:15 +0200	[thread overview]
Message-ID: <CAOMqctSn-Ct06tWqSVYPbdoXcFmwrLb1Y9MGvhsSz0gf+fRP3Q@mail.gmail.com> (raw)
In-Reply-To: <201505010113.50293.marex@denx.de>

On 1 May 2015 at 01:13, Marek Vasut <marex@denx.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@gmail.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.

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

Thanks

Michal