Re: [PATCH 3/4] pinctrl: mcp23s08: debugfs: Do not restore the INTF register

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Tue, Feb 20, 2018 at 7:04 PM, Jan Kundrát <jan.kundrat@xxxxxxxxx> wrote:

> Apart from the usual stuff, the debugfs code is currently also used for
> one non-obvious side effect. It attempts to check whether the chip's
> registers are still set to an expected value, and if not, re-initializes
> them. It seems that the driver has "always" done so.
>
> The code, however, also checks the INTF register which normally
> indicates which pins have caused the recent interrupt. That's a volatile
> register, and the datasheet says that writes are ignored in there.
>
> When I'm just cat-ing /sys/kernel/debug/gpio with no SPI traffic and no
> nosie on the GPIO lines, I'm not getting any warnings. Once I actually
> use these GPIOs and cat that file in parallel, I always seem to get a:
>
>   mcp23s08 spi1.1: restoring reg 0x07 from 0x0000 to 0xffff (power-loss?)
>
> This might be a sign that I should not leave my unused inputs floating,
> but the code should not be checking a volatile register, anyway. Let's
> simply skip this last item in the iteration. I was also considering
> removing this enitre re-initialization because it's non-obvious, but the
> code survived various refactorings already and has sign-offs by people
> who know more than I do, so let's leave it as-is. For now :).
>
> Signed-off-by: Jan Kundrát <jan.kundrat@xxxxxxxxx>

Patch applied with Phil's review tag.

Yours,
Linus Walleij
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