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Date: Tue, 27 Jun 2006 11:02:52 +0400
From: "Artem B. Bityutskiy" <dedekind@yandex.ru>
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To: David Brownell <david-b@pacbell.net>
Subject: Re: DataFlash & writesize
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Hello David,

David Brownell wrote:
> What are the intended semantics for "writesize" by the way?
Design-wise, it an attempt to generalize MTD. Different flashes have 
different minimal I/O unit size, like 1 byte in case of NOR, 16 bytes in 
case of ECCed NOR, 512/2K in case of NAND, etc. There were no such a 
field before and we had to do ugly things like


switch (mtd->type) {
	case MTD_NORFLASH:
		blah();
		break;
	case MTD_NANDFLASH:
		blah1();

etc.

Here is a comment from include/linux/mtd.h:

/* Minimal writable flash unit size. In case of NOR flash it is 1 (even
  * though individual bits can be cleared), in case of NAND flash it is
  * one NAND page (or half, or one-fourths of it), in case of ECC-ed NOR
  * it is of ECC block size, etc. It is illegal to have writesize = 0.
  * Any driver registering a struct mtd_info must ensure a writesize of
  * 1 or larger.
  */

> 
> I noticed I was getting that first BUG_ON in mtdcore:add_mtd_device
> since, with NOR CFI cmdset 1 flash, with current GIT.  Seems like
> writesie should have been set up already.

We fixed all drivers and now it should be fine - see commit 
17ffc7ba6d7ea68b8d5f55a5ca1b87163e69720d

-- 
Best Regards,
Artem B. Bityutskiy,
St.-Petersburg, Russia.