Re: [PATCH 2/2] fsl-quadspi: introduce per-bus spi-bus-width property

On Tue, Oct 18, 2016 at 10:03 PM, Albert ARIBAUD
[off-list ref] wrote:

Le Mon, 3 Oct 2016 21:57:58 +0200, Geert Uytterhoeven
[off-list ref] a écrit :

quoted

On Mon, Oct 3, 2016 at 8:51 PM, Rob Herring [off-list ref] wrote:

quoted

On Tue, Sep 27, 2016 at 07:59:57AM +0200, Albert ARIBAUD (3ADEV) wrote:

quoted

Introduce spi-bus-width property for bus subnodes, to
specify per-bus capability to use NORMAL, FAST, DUAL,
and/or QUAD reads.

Signed-off-by: Albert ARIBAUD (3ADEV) <redacted>
---
 Documentation/devicetree/bindings/mtd/fsl-quadspi.txt | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Make this a common property.

@Rob: do you mean common to all slaves, i.e. described
in ./Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt?

quoted

They already exist:

Documentation/devicetree/bindings/spi/spi-bus.txt:
- spi-tx-bus-width - (optional) The bus width (number of data wires)
that is used for MOSI. Defaults to 1 if not present.
- spi-rx-bus-width - (optional) The bus width (number of data wires)
that is used for MISO. Defaults to 1 if not present.

The above are for normal/dual/quad.

"Fast" is not a property of the bus, but of the SPI slave, right? Cfr.

Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt:
- m25p,fast-read : Use the "fast read" opcode to read data from the
chip instead of the usual "read" opcode. This opcode is not supported
by all chips and support for it can not be detected at runtime.
                   Refer to your chips' datasheet to check if this is
supported by your chip.

Gr{oetje,eeting}s,

@Geert: the problem here is that on the board for which I wrote this
patch, only one of the two NOR slaves can do quad SPI; the other one
can do dual at best. Setting a bus property would prevent the
quad-capable device from doing actual quad reads.

The fsl-quadspi driver already supports per-NOR read and erase commands
to support heterogeneous NOR setups. A per-NOR bus width property would
make sense in this light.

spi-[tx]x-bus-width is already a property for the SPI slave, not for
the whole bus.
So you can use 4 for the quad-capable device, and 1 or 2 for the other.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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