Hi, Tomasz

2013/8/31 Tomasz Figa [off-list ref]:

Hi,

[Ccing DT binding maintainers]

On Tuesday 27 of August 2013 08:50:03 wangyuhang wrote:

quoted

Add spi-tmax-nbits and spi-rmax-nbits for spi slave node.
Modify the related dt document(spi-bus.txt)
 spi-tmax-nbits:Max number of bits slave will use for MOSI(writting)
 spi-rmax-nbits:Max number of bits slave will use for MISO(reading)
Support for spi-tx/rmax-nbits in SPI framework has been picked[1].
[1]: http://comments.gmane.org/gmane.linux.kernel.spi.devel/14420
Commit Id:f477b7fb13df2b843997559ff34e87d054ba6538

Signed-off-by: wangyuhang <redacted>
---
 Documentation/devicetree/bindings/spi/spi-bus.txt |   16
++++++++++++++++ 1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt

b/Documentation/devicetree/bindings/spi/spi-bus.txt index
296015e..211336c 100644

--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt

@@ -55,6 +55,22 @@ contain the following properties.
              chip select active high
 - spi-3wire       - (optional) Empty property indicating device

requires 3-wire mode.
+- spi-tmax-nbits  - (optional) Max number of bits slave will use for
+                 MOSI(writting)
+- spi-rmax-nbits  - (optional) Max number of bits slave will use for
+                 MISO(reading)

May I ask for more human-readable names, please?

If we look around, there are already devices using bus-width property, so
for consistency we could use tx-bus-width and rx-bus-width here or even a
single bus-width property taking two cells, first tx and second rx?

Yes, you are right. bus_width is really more widely used. So I will correct it.

Let's hear others' opinion on this as well.

Also the properties should be telling information about hardware, so
probably in this case the meaning would be the number of wires that are
physically wired on the board.

quoted

+

One or two sentences about what this dual/quad thing is about would be
nice here, e.g.

        Some SPI controllers and devices support Dual and/or Quad SPI
        mode, which is [...]. It allows [...], etc.

OK, Thanks.

quoted

+So if for example the slave has 4 wires for writting and 2 wires for
reading, +and the spi-tx/rx-nbits property should be set as follows:
+
+spi-tmax-nbits = <4>;
+spi-rmax-nbits = <2>;
+
+Now the value that spi-tmax-nbits and spi-rmax-nbits can receive is
only +1(single), 2(dual) and 4(quad). If you don't set spi-tmax-nbits
or spi-rmax-nbits, +spi_device mode will be set in single(1 wire) as
default. Another point, if +property:spi-3wire is set, spi-t/rmax-nbits
is forbidden to set to <2 or 4>, +otherwise, an errro will return.

typo: errro

Also an error or "returning an error" is an OS specific term. This
statement should rather be something along

        Dual/Quad mode is not allowed when 3-wire mode is used.

Got it, Thanks a lot.

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