On 04/04/2014 10:09 AM, Geert Uytterhoeven wrote: > Hi Harini, > > On Fri, Apr 4, 2014 at 5:00 AM, Harini Katakam > <harinikatakamlinux@xxxxxxxxx> wrote: >>>> + num-cs = /bits/ 16 <4>; >>> >>> What's going on with the /bits/ - is this something that's required for >>> the property? >> >> The master->num-chipselect property is 16 bit but writing <4> here directly >> leads to 0 being read in of_property_read (because it's big endian). >> Instead using of property read u32 and then copying, we decided to do this. >> This was discussed on v2 between Michal and Rob: >>>>>> + num-chip-select = /bits/ 16 <4>; >>>> >>>> I was expecting you will comment this a little bit. :-) >>>> Because all just reading this num-cs as 32bit and then >>>> assigning this value to master->num_chipselect which is 16bit. >>> >>> Well, everyone else has that problem then. Obviously it takes a bit >>> more care than just reading into a u32, but that is a kernel problem >>> and not a problem of the binding. >> They are not reading it directly with read_u32 but they are using >> intermediate u32 value which is assigned to u16 which is fine. >> This pattern is in most drivers(maybe all). >> The point is if binding should or can't simplify driver code. >> And from your reaction above I expect that it is up to driver >> owner and binding doc how you want to do it. > > IMHO this "/bits/ 16" doesn't simplify the binding. > > As "num-cs" is a generic spi subsystem binding, it should not be > restricted to 16 bits for the sake of a driver. As your hardware can drive 4 > chip selects, you could represent it in 3 bits (don't!). > > Simple integers are 32 bit in DT, so use a temporary. No problem to keep it there to 32bit range. I really appreciate that discussion we have about it. Just a note: If "num-cs" is the part of generic spi subsystem binding maybe it should be moved directly to spi core as is done for example for timeout-sec in watchdog. Also this should be listed in any Documentation/devicetree/bindings/spi/spi.txt file that this is generic spi binding. Thanks, Michal -- Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91 w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/ Maintainer of Linux kernel - Xilinx Zynq ARM architecture Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform
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