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 12:50:04 +0200
From:	Jonas Gorski <jogo@...nwrt.org>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	Marek Vasut <marex@...x.de>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	David Woodhouse <dwmw2@...radead.org>,
	"Rafa?? Mi??ecki" <zajec5@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	"grmoore@...era.com" <grmoore@...era.com>,
	Brian Norris <computersforpeace@...il.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Alison Chaiken <alison_chaiken@...tor.com>,
	"Bean Huo (beanhuo)" <beanhuo@...ron.com>
Subject: Re: [PATCH 3/3] MTD: spi-nor: add flag to not use sector erase.

Hi,

On Fri, May 1, 2015 at 9:05 AM, Michal Suchanek <hramrach@...il.com> 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.
>
> It's a value that we don't use anyway so I just mark it as unknown
> here for future reference.

It will be used if MTD_SPI_NOR_USE_4K_SECTORS is unset, so you should
add some code to properly handle that case.

Also I'd suggest switching the order of 2 and 3, so you add the flag
handling first and then add support for a flash chip with this issue.


Regards
Jonas
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