[PATCH 4/6] mtd: m25p80: change the read function to read page by page

[Hu Mingkai-B21284]

> -----Original Message-----
> From: Grant Likely [mailto:glikely at secretlab.ca] On Behalf Of 
> Grant Likely
> Sent: Monday, July 26, 2010 8:30 AM
> To: Hu Mingkai-B21284
> Cc: linuxppc-dev at ozlabs.org; galak at kernel.crashing.org; Zang 
> Roy-R61911
> Subject: Re: [PATCH 4/6] mtd: m25p80: change the read 
> function to read page by page
> 
> On Tue, Jul 20, 2010 at 10:08:23AM +0800, Mingkai Hu wrote:
> > For Freescale's eSPI controller, the max transaction length 
> one time 
> > is limitted by the SPCOM[TRANSLEN] field which is 0x10000. When used
> > mkfs.ext2 command to create ext2 filesystem on the flash, the read 
> > length will exceed the max value of the SPCOM[TRANSLEN] field, so 
> > change the read function to read page by page.
> > 
> > For other SPI flash driver, also needed to change the read 
> function if 
> > used the eSPI controller.
> > 
> > Signed-off-by: Mingkai Hu <Mingkai.hu at freescale.com>
> > ---
> >  drivers/mtd/devices/m25p80.c |   18 ++++++++++++++----
> >  1 files changed, 14 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/mtd/devices/m25p80.c 
> > b/drivers/mtd/devices/m25p80.c index 81e49a9..6cbe6b1 100644
> > --- a/drivers/mtd/devices/m25p80.c
> > +++ b/drivers/mtd/devices/m25p80.c
> > @@ -317,6 +317,7 @@ static int m25p80_read(struct mtd_info 
> *mtd, loff_t from, size_t len,
> >  	struct m25p *flash = mtd_to_m25p(mtd);
> >  	struct spi_transfer t[2];
> >  	struct spi_message m;
> > +	u32 i, page_size = 0;
> >  
> >  	DEBUG(MTD_DEBUG_LEVEL2, "%s: %s %s 0x%08x, len %zd\n",
> >  			dev_name(&flash->spi->dev), __func__, 
> "from", @@ -341,7 +342,6 @@ 
> > static int m25p80_read(struct mtd_info *mtd, loff_t from, 
> size_t len,
> >  	spi_message_add_tail(&t[0], &m);
> >  
> >  	t[1].rx_buf = buf;
> > -	t[1].len = len;
> >  	spi_message_add_tail(&t[1], &m);
> >  
> >  	/* Byte count starts at zero. */
> > @@ -364,11 +364,21 @@ static int m25p80_read(struct mtd_info *mtd, 
> > loff_t from, size_t len,
> >  
> >  	/* Set up the write data buffer. */
> >  	flash->command[0] = OPCODE_READ;
> > -	m25p_addr2cmd(flash, from, flash->command);
> >  
> > -	spi_sync(flash->spi, &m);
> > +	for (i = page_size; i < len; i += page_size) {
> > +		page_size = len - i;
> > +		if (page_size > flash->page_size)
> > +			page_size = flash->page_size;
> >  
> > -	*retlen = m.actual_length - m25p_cmdsz(flash) - 
> FAST_READ_DUMMY_BYTE;
> > +		m25p_addr2cmd(flash, from + i, flash->command);
> > +		t[1].len = page_size;
> > +		t[1].rx_buf = buf + i;
> > +
> > +		spi_sync(flash->spi, &m);
> > +
> > +		*retlen += m.actual_length - m25p_cmdsz(flash)
> > +			- FAST_READ_DUMMY_BYTE;
> > +	}
> 
> This patch seems to cripple all users just because eSPI 
> cannot handle it.  Am I reading it wrong?
> 

You're right, this will cripple all users.

At first, I want to contain this specific code with CONFIG_SPI_FSL_ESPI
option,
or register a specific read function like:

#ifdef CONFIG_SPI_FSL_ESPI
        flash->mtd.read = m25p80_read_espi;
#endif

but this will make the code looks arguly, are there other ways?

Thanks,
Mingkai