[PATCH V5] mtd: m25p80: Make fast read configurable via DT

[Kevin Cernekee]

On Sat, Aug 25, 2012 at 12:36 PM, Marek Vasut <marex at denx.de> wrote:
> Add DT property "m25p,fast-read" that signalises the particular
> chip supports "fast read" opcode.

This might be slightly clearer if it is rephrased as:

Add DT property "m25p,fast-read" that signifies whether the "fast
read" opcode is supported.

> +Optional properties:
> +- m25p,fast-read : Use the "fast read" opcode to read data from the chip instead
> +                   of the usual "read" opcode. This opcode isn not supported by
> +                   all chips and support for it can not be detected at runtime.

"is not supported"

Are there any modern SPI flash parts that can't handle FAST_READ, or
is this mostly for compatibility with legacy systems?

> +       bool                    fast_read;

> -       t[0].len = m25p_cmdsz(flash) + FAST_READ_DUMMY_BYTE;
> +       t[0].len = m25p_cmdsz(flash) + (flash->fast_read ? 1 : 0);

Newer devices support a variable number of dummy cycles; increasing
the number of dummy cycles can allow for higher interface speeds.  One
example is the Macronix MX25L25635F:

http://bit.ly/P9s7UM

It might be worth thinking about how to capture this sort of
information in the DT properties, even if current versions of m25p80
only use a small subset of the device capabilities.