support DUAL and QUAD[patch v1]

[thomas.langer at lantiq.com]

Hello Huang,

Huang Shijie wrote on 2013-07-22:
> 于 2013年07月22日 17:56, Gupta, Pekon 写道:
>> (b) struct spi_transfer: if each transfer of same message need to be
>> transferred at different width. 	Example: Command @ Single-SPI
>>   followed by Data @ Quad-SPI
> I am coding the QuadSpi driver for Freescale's Vybrid now.
> 
> I think we dot need to change the spi code. the spi layer should not
> know the different width of the command and the data, let the qspi
> driver does it.
NO!
> 
> In the m25p_probe(), after we knows that the qspi driver and flash
> support the Quad read, so we can set the
> m25p->read_opcode to 0xeb or 0xec. In the qspi driver, it can do the
> real job.
No, the qspi driver (as example here) should provide a transparent interface only,
and the mp25p80 driver, which knows the details of the flash, has to provide the information
which parts of a transfer has to be done in single-/dual- or quad-mode.
Otherwise you always need to extend the qspi driver for new flashes.

> 
> thanks
> Huang Shijie
> 
Best Regards,
Thomas