Hello.
> On Tue, Dec 10, 2013 at 4:26 PM, Alexander Shiyan <shc_work@xxxxxxx> wrote:
>
> > SYSCON driver was designed for using memory areas (registers)
> > that are used in several subsystems. There are systems (CPUs)
> > which use bits in one register for various purposes and thus
> > should be handled by various kernel subsystems. This driver
> > allows you to use the individual SYSCON bits as GPIOs.
> >
> > Signed-off-by: Alexander Shiyan <shc_work@xxxxxxx>
> (...)
> > ---
> > +Required properties:
> > +- compatible: Should be "gpio-syscon".
> > +- syscon: Phandle to syscon device node.
> > +- gpio-controller: Marks the device node as a gpio controller.
> > +- #gpio-cells: Should be two. The first cell is the pin number and
> > + the second cell is used to specify the gpio polarity:
> > + 0 = Active high,
> > + 1 = Active low.
> > +- bit-offset: Offset to the first bit used by driver.
> > +- bit-count: Number of bits used.
> > +
> > +Example:
> > + sysgpio: sysgpio {
> > + compatible = "gpio-syscon";
> > + syscon = <&syscon>;
> > + gpio-controller;
> > + #gpio-cells = <2>;
> > + bit-offset = <4>;
> > + bit-count = <1>;
>
> I take it that bit-offset can be say 1024 and bit count
> 32 for a 32-bit register at syscon_base + 0x80?
This can be represented in DT as (0x80 << 4).
> I have a real big problem with encoding register offsets into
> the device tree as I have stated before, it is starting to
> get real hard to debug this, like:
>
> "hmmm where did this go wrong?"
>
> "in the byte offset from the base stored in this
> other driver plus ... 1024? no wait, that is stored
> it bit notation so I need to divide by 8 ... hm which
> was it now ... and where do I have all these figures
> in my ICE debugger?"
>
> The code is not helpful anymore, you have to go in
> and reverse-engineer this and bring up a calculator
> to figure out what is going on.
>
> I sort of like the syscon driver but I don't like the idea
> of encoding register offsets into the device tree, even
> less do I like the idea of encoding it in bit notation.
I also have no idea how to present it differently.
Can try to specify the byte offset through the "reg" property?
The "bit-offset" will remain, but will point offset from the "reg" byte.
> I prefer that you put a header with all the offsets
> into <linux/mfd/syscon-foo.h> and define all the
> offsets there, then to reuse this driver with several
> GPIO controllers all doing this GPIO-in-syscon
> business, to #include <linux/mfd/syscon-bar.h>
> etc and use the compatible string to figure out
> which file to pick the offsets from.
No headers is needed. Driver will be used in DTS only.
...
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