linux-kernel - Re: [PATCH 20/49] regmap-irq: Fix inverted handling of unmask registers

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Date:   Tue, 21 Jun 2022 11:40:12 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Aidan MacDonald <aidanmacdonald.0x0@...il.com>
Cc:     Mark Brown <broonie@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Banajit Goswami <bgoswami@...eaurora.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
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        MyungJoo Ham <myungjoo.ham@...sung.com>,
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Subject: Re: [PATCH 20/49] regmap-irq: Fix inverted handling of unmask registers

On Mon, Jun 20, 2022 at 10:08 PM Aidan MacDonald
<aidanmacdonald.0x0@...il.com> wrote:
>
> To me "unmask" suggests that we write 1s to the register when
> an interrupt is enabled. This also makes sense because it's the
> opposite of what the "mask" register does (write 1s to disable
> an interrupt).
>
> But regmap-irq does the opposite: for a disabled interrupt, it
> writes 1s to "unmask" and 0s to "mask". This is surprising and
> deviates from the usual way mask registers are handled.
>
> Additionally, mask_invert didn't interact with unmask registers
> properly -- it caused them to be ignored entirely.
>
> Fix this by making mask and unmask registers orthogonal, using
> the following behavior:
>
> * Mask registers are written with 1s for disabled interrupts.
> * Unmask registers are written with 1s for enabled interrupts.
>
> This behavior supports both normal or inverted mask registers
> and separate set/clear registers via different combinations of
> mask_base/unmask_base. The mask_invert flag is made redundant,
> since an inverted mask register can be described more directly
> as an unmask register.
>
> To cope with existing drivers that rely on the old "backward"
> behavior, check for the broken_mask_unmask flag and swap the
> roles of mask/unmask registers. This is a compatibility measure
> which can be dropped once the drivers are updated to use the
> new, more consistent behavior.

...

> +                       if (ret != 0)

if (ret)

> +                               dev_err(d->map->dev, "Failed to sync masks in %x\n",
> +                                       reg);

...

> +                       if (ret != 0)

Ditto.

> +                               dev_err(d->map->dev, "Failed to sync masks in %x\n",

...

> +       /*
> +        * Swap role of mask_base and unmask_base if mask bits are inverted.

the roles

> +        *
> +        * Historically, chips that specify both mask_base and unmask_base
> +        * got inverted mask behavior; this was arguably a bug in regmap-irq
> +        * and there was no way to get the normal, non-inverted behavior.
> +        * Those chips will set the broken_mask_unmask flag. They don't set
> +        * mask_invert so there is no need to worry about interactions with
> +        * that flag.
> +        */

Reading this comment perhaps the code needs a validator part that will
issue a WARN_ON / dev_warn() / etc in case where the above is not
satisfied?

...

> +                       if (ret != 0) {

if (ret)


> +                               dev_err(map->dev, "Failed to set masks in 0x%x: %d\n",
> +                                       reg, ret);

...

> +                       if (ret != 0) {

Ditto.

> +                               dev_err(map->dev, "Failed to set masks in 0x%x: %d\n",
> +                                       reg, ret);

-- 
With Best Regards,
Andy Shevchenko