[PATCH V2] SPI: DUAL and QUAD support

[Mark Brown]

On Mon, Jul 29, 2013 at 10:44:43AM +0800, yuhang wang wrote:

> > Your changes to spidev are not backward compatible at all.  You can
> > not change the data types in the ioctl and maintain backward
> > compatibility.  You can also not delete ioctls!

> well, please give me some details or specific situations. Why ioctl
> can not be changed. The operation that SPI_IOC_RD_LSB_FIRST do can be
> done in SPI_IOC_RD_MODE, so I dont think there is any necessary using
> SPI_IOC_RD_LSB_FIRST. What you worry about is the user already used
> SPI_IOC_RD_LSB_FIRST?

You need to make sure that existing userspace binaries can run
unmodified, changing the types will change the layout of the ioctl
arguments.  This may mean that you need to add new ioctls if you need to
change types.
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