Re: [PATCH v3 14/36] mtd: st_spi_fsm: Add device-tree binding documentation

Linus Walleij
2013-12-03T10:23:41Z

On Mon, Dec 2, 2013 at 12:03 PM, Lee Jones <lee.jones@linaro.org> wrote:
>> > +Optional properties:
>> > + - st,syscfg : Phandle to boot-device system configuration registers
>> > + - st,boot-device-reg : Address of the aforementioned boot-device register(s)
>> > + - st,boot-device-spi : Expected boot-device value if booted via this device
>> > +
>> > +Example:
>> > + spifsm: spifsm@fe902000{
>> > + compatible = "st,spi-fsm";
>> > + reg = <0xfe902000 0x1000>;
>> > + reg-names = "spi-fsm";
>> > + pinctrl-0 = <&pinctrl_fsm>;
>> > + st,syscfg = <&syscfg_rear>;
>> > + st,boot-device-reg = <0x958>;
>> > + st,boot-device-spi = <0x1a>;
>>
>> I don't think we should encode any register offsets whatsoever in device
>> tree but maybe that's just me. (Yes, Stephen will beat me up about
>> pin control single, but I consider that a special case.)
>>
>> I would just put the last two things as #defines into the driver file(s)
>> or - if it's related to other syscfg registers and varies with SoC incarnation,
>> as a #define in a shared header for that syscfg thing.
>
> No can do. This isn't _this_ device's register offset, this is a
> syscfg register offset which a) there is no driver to apply specific
> register offsets to and b) are liable to change oversubsequent SoCs.

So it can be in <linux/mfd/my-sysconfig-regs.h> as
a

#define MY_SYSCON_V1_BOOT_DEV_REG 0x958
#define MY_SYSCON_V1_BOOT_DEV_SPI 0x1a

The kernel should know which SoC is in use and
act apropriately right?

But indeed, what you're doing has been done before
in drivers/regulator/anatop-regulator.c where some
register offset is read in from the attribute
"anatop-delay-reg-offset". So it may be that the DT people
need to overrule me on this one :-)

I don't think we should hard-code knowledge of specific
register locations into the device tree at all as that makes
things very hard to debug.

Yours,
Linus Walleij