Messages in this thread | | | Date | Fri, 27 Mar 2015 11:55:49 +0100 | From | Michal Simek <> | Subject | Re: [PATCH] spi: xilinx: Use standard num-cs binding |
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Hi Mark,
On 03/08/2015 08:00 PM, Mark Brown wrote: > On Fri, Jan 16, 2015 at 01:55:14PM +0100, Michal Simek wrote: >> Use standard num-cs binding property and setup >> "xlnx,num-ss-bits" as deprecated. > > Why? These properties mean different things - num-cs is a bit confused > and is the total number of available chip selects for the system (which > could include GPIOs) while num-ss-bits is the size of the bitfield > (which could include things not actually mapped out properly/successfully > or something if the hardware designers were feeling particularly inspired).
I was checking meaning of num-ss-bits and meaning is Number of slaves (taking explanation from Vivado 2014.4) Range 1-32. http://www.xilinx.com/support/documentation/ip_documentation/axi_spi/v1_02_a/axi_spi_ds742.pdf Table 1 - page 4
Checking through the hw design every pin is connected to device to do chip select. That's why I think that num-cs (based on spi-bus.txt) is the right property.
Of course hw guys can use decoder from these bits and we could use binding as is used in cadence spi (is-decoded-cs)
> I'm not convinced num-cs ever made any sense.
Does it mean that num-cs property used by 11 SPI drivers is just incorrect?
Based on Documentation/devicetree/bindings/spi/spi-bus.txt it is the part of binding - num-cs : total number of chipselects
Please let me know what you think.
Thanks, Michal
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