[PATCH 12/30] staging: comedi: dmm32at: use 8255 module for Digital I/O subdevice

[Ian Abbott]

On 11/11/14 23:55, H Hartley Sweeten wrote:
> The Dimond-MM-32-AT board uses an internal 82C55-type digital I/O circuit to
> provide the 24 digital I/O lines. The only quirk is the need to set the page
> selection bits in the control register to select page 1 addresses.
>
> Instead of duplicating the 8255 code, provide an (*io) callback and use the
> 8255 module to support this subdevice.
>
> This also removes the need for the private data in this driver.

The patch is fine, but there's a bug in the original code which means we 
might need the private data back (unless the DMM32AT_CNTRL register is 
read-write rather than read-only).  The bug is that the ISR routine 
clobbers the page selection bits in the register.  To avoid that, the 
current page would either need to be stored in private data or read from 
the register (if possible) to avoid clobbering it, and updates to the 
register would need a spin-lock.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti at mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-