linux-kernel - Re: [RFC PATCH] MTD: atmel_nand: optimize read/write buffer functions

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Message-ID: <20110628145937.GG21898@n2100.arm.linux.org.uk>
Date:	Tue, 28 Jun 2011 15:59:37 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>, hong.xu@...el.com,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH] MTD: atmel_nand: optimize read/write buffer
	functions

On Tue, Jun 28, 2011 at 01:10:43PM +0200, Uwe Kleine-König wrote:
> > @@ -265,33 +234,53 @@ err_buf:
> >  static void atmel_read_buf(struct mtd_info *mtd, u8 *buf, int len)
> >  {
> >  	struct nand_chip *chip = mtd->priv;
> > -	struct atmel_nand_host *host = chip->priv;
> > +	u32 align;
> > +	u8 *pbuf;
> >  
> >  	if (use_dma && len > mtd->oobsize)
> >  		/* only use DMA for bigger than oob size: better performances */
> >  		if (atmel_nand_dma_op(mtd, buf, len, 1) == 0)
> >  			return;
> >  
> > -	if (host->board->bus_width_16)
> > -		atmel_read_buf16(mtd, buf, len);
> > -	else
> > -		atmel_read_buf8(mtd, buf, len);
> > +	/* if no DMA operation possible, use PIO */
> > +	pbuf = buf;
> > +	align = 0x03 & ((unsigned)pbuf);
> > +
> > +	if (align) {
> > +		u32 align_len = 4 - align;
> > +
> > +		/* non aligned buffer: re-align to next word boundary */
> > +		ioread8_rep(chip->IO_ADDR_R, pbuf, align_len);
> > +		pbuf += align_len;
> > +		len -= align_len;
> > +	}
> > +	memcpy((void *)pbuf, chip->IO_ADDR_R, len);
> I think you don't need to cast to (void *). I think you need to cast the
> 2nd parameter instead because sparse don't like you passing an void
> __iomem *.
> Is it correct to read from chip->IO_ADDR_R, don't you need
> chip->IO_ADDR_R + align_len? Taking this into account, does it really
> help to align pbuf?

I think you need to read Documentation/bus-virt-phys-mapping.txt,
particularly the part after "NOTE NOTE NOTE".

Dereferencing ioremap'd memory is not permitted.  That includes passing
it to memcpy.  Even with a cast.
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