RE: [PATCH 2/3] gpio: gpio-rz: GPIO driver for Renesas RZ series

[Chris Brandt <Chris.Brandt@xxxxxxxxxxx>]

Hi Jacopo,

On Thursday, January 12, 2017, jacopo mondi wrote:
> To read the pin direction I would need to add one more register to the
> "reg" property range provided in the DTS.
> This is of course doable, but I would have two questions here:
> - why did you chose to use PMSR register instead of reading/writing
> directly to PM? Am I missing something?


I guess you can still use the PMSR register to get the current direction
of the I/O pin. According to the HW manual:

"When reading, the higher 16 bits are read as 0000H. The lower 16 bits
 are read as the value of the PMn register."


While the PMSR register is a cool idea of having a special register that
can change a single port pin direction without doing a read-modify-write
by the CPU, it doesn't seem to be a standard option in Renesas SoCs (well,
except for the older NEC V850 parts where this PFC HW came from).
So a more traditional method of just using the Pmn register seems to be
more compatible across Renesas SoCs.


Chris

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