SPI: DUAL/QUAD support

[Johannes Stezenbach]

On Fri, Jul 05, 2013 at 06:24:40PM +0800, yuhang wang wrote:
> 
> 2 Questions here:
> 1.In m25p80.c probe, the kmalloc below I feel very strange.
>       flash->command = kmalloc(MAX_CMD_SIZE + (flash->fast_read ? 1 : 0),
>                                       GFP_KERNEL);
> 
>  (flash->fast_read ? 1 : 0) must be 0! So why do it like that.

Maybe just increase MAX_CMD_SIZE by 1 unconditonally?
Yeah, looks like a bug in m25p80.c, flash->fast_read
is initialized too late.

> +#define        OPCODE_DOR              0x3B    /* Dual Output Read */
> +#define        OPCODE_QOR              0x6B    /* Quad Output Read */
> +#define        OPCODE_QPP              0x32    /* Quad Page Programming */
> +#define        OPCODE_QEN              0x02 /* Quad Mode Enable Flag */

Which flash chip are these for?  The OPCODE_DOR and OPCODE_QOR
match MX25L25635E, but OPCODE_QPP not (Macronix uses 0x38).



> +#ifdef CONFIG_M25PXX_USE_FAST_READ
> +#define OPCODE_READ    OPCODE_FAST_READ
> +#define FAST_READ_DUMMY_BYTE 1
> +#else
> +#define OPCODE_READ    OPCODE_NORM_READ
> +#define FAST_READ_DUMMY_BYTE 0
> +#endif

this doesn't work with the flash->fast_read setting from DT

BTW, if we add "bitwidths" to spi_board_info, wouldn't
it make sense to also add "use_fast_read" and remove the
CONFIG_M25PXX_USE_FAST_READ option?

> +/*
> + * Write configuration register 2 byte
> + * Returns negative if error occurred.
> + */
> +static int write_cr(struct m25p *flash, u16 val)
> +{
> +       flash->command[0] = OPCODE_WRSR;
> +       flash->command[1] = val >> 8;
> +       flash->command[2] = val;
> +
> +       return spi_write(flash->spi, flash->command, 3);
> +}

> +       if ((flash->spi->rx_bitwidth == SPI_BITWIDTH_QUAD) ||
> +               (flash->spi->tx_bitwidth == SPI_BITWIDTH_QUAD)) {
> +               write_enable(flash);
> +               write_cr(flash, OPCODE_QEN);
> +       }

MX25L25635E doesn't have a cr, instead a bit needs to be set in the sr

Maybe we need to add some fields to m25p_ids[] to manage variation
between flash devices.


Thanks,
Johannes