Subject: [PATCH V2 2/4] mtd: spi-nor: add the basic data structures

From: [email-masked] (Huang Shijie)
Date: Wed, 11 Dec 2013 22:33:58 +0800

On Wed, Dec 11, 2013 at 11:02:18AM +0100, Marek Vasut wrote:
> > > > +
> > > > +	/* the two fundamental primitives */
> > > > +	int (*read_xfer)(struct spi_nor *nor, struct spi_nor_xfer_cfg *cfg,
> > > > +			 u8 *buf, size_t len);
> > > > +	int (*write_xfer)(struct spi_nor *nor, struct spi_nor_xfer_cfg *cfg,
> > > > +			  u8 *buf, size_t len);
> > > > +
> > > > +	int (*read_reg)(struct spi_nor *nor, u8 opcode, u8 *buf, int len);
> > > > +	int (*write_reg)(struct spi_nor *nor, u8 opcode, u8 *buf, int len,
> > > > +			int write_enable);
> This stuff -- I mean 'read SPI NOR register' and 'write SPI NOR register'. I 
> would love to see an API which grows as needed, not an API which is bloated by 
> unused function right from the start.
I should send out my fsl-quadspi driver in the next version.

The read_reg/write_reg are implemented by the m25p80 and fsl-quadspi
now.

I think Lee's driver can implemente the read_xfer/write_xfer.

> 
> > > > +	const struct spi_device_id *(*read_id)(struct spi_nor *nor);
> > > > +	int (*wait_till_ready)(struct spi_nor *nor);
> > > > +
> > > > +	/* write */
> > > > +	void (*write)(struct spi_nor *nor, loff_t to,
> > > > +			size_t len, size_t *retlen, const u_char *buf);
> > > > +	/* read */
> > > > +	int (*read)(struct spi_nor *nor, loff_t from,
> > > > +			size_t len, size_t *retlen, u_char *buf);
> > > > +	/* erase */
> > > > +	int (*erase)(struct spi_nor *nor, loff_t offs);
> > > 
> > > How do you specify what to erase (sub-sector, sector, whole chip) here ?
> > 
> > I use a write_reg(OPCODE_ERASE_CHIP) to erase the whole chip.
> > Please read the patch 3.
> > 
> > This hook is used to erase a sector.
> 
> I suspect we might need a much better documentation for this structure, it is 
> hardly clear which function does what ;-)

sorry, i will add more comment in the next version.

> 
> > Btw, what is the sub-sector mean? which opcodes for the sub-sector?
> 
> On large chips with for example 64K big sectors, you can erase a sub-sector 
> area, usually a 4K one. This reduces the wear of the chip. See these defines in 
> m25p80.c :
> 
>   46 #define OPCODE_BE_4K            0x20    /* Erase 4KiB block */
>   48 #define OPCODE_BE_32K           0x52    /* Erase 32KiB block */
>   49 #define OPCODE_CHIP_ERASE       0xc7    /* Erase whole flash chip */
ok.

the @erase hook can be used for sub-sector too.

thanks
Huang Shijie