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Date: Thu, 28 Feb 2013 11:48:19 +0100
From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= <u.kleine-koenig@pengutronix.de>
To: Huang Shijie <b32955@freescale.com>
Subject: Re: [PATCH] mtd/nand: don't use {read,write}_buf for 8-bit transfers
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On Thu, Feb 28, 2013 at 10:47:43AM +0800, Huang Shijie wrote:
> 于 2013年02月27日 23:10, Uwe Kleine-König 写道:
> >According to the Open NAND Flash Interface Specification (ONFI) Revision
> >3.1 "Parameters are always transferred on the lower 8-bits of the data
> >bus." for the Get Features and Set Features commands.
> >
> yes. the set/get features should works in 8-bit.
> 
> I have never met a 16-bit onfi nand yet. :)
> 
> >So using read_buf and write_buf is wrong for 16-bit wide nand chips as
> >they use I/O[15:0]. The Get Features command is easily fixed using 4
> >times the read_byte callback. For Set Features error out as there is no
> yes. for get features, it's easy to fix it.
> >write_byte callback.
> Most of the time, the nand controller will overwrite the write_buf hook...
> I also think we need a write_byte callback.
a default implementation could be something like that:

	static void nand_write_byte(struct mtd_info *mtd, uint8_t byte)
	{
		struct nand_chip *chip = mtd->priv;

		if (chip->options & NAND_BUSWIDTH_16)
			chip->write_buf(mtd, (uint8_t[]){ byte, 0 }, 2);
		else
			chip->write_buf(mtd, &byte, 1);
	}

(Is this the correct order in the array? Or might that depend on
endianess?)

Does this look right?

Alternatively something could be done with chip->cmd_ctrl (but it seems
not all drivers implement this, e.g. mxc_nand doesn't).

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |