linux-kernel - Re: [PATCH 15/49] regmap-irq: Change the behavior of mask

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Date:   Tue, 21 Jun 2022 11:29:23 +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>,
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Subject: Re: [PATCH 15/49] regmap-irq: Change the behavior of mask_writeonly

On Mon, Jun 20, 2022 at 10:08 PM Aidan MacDonald
<aidanmacdonald.0x0@...il.com> wrote:
>
> No drivers currently use mask_writeonly, and in its current form
> it seems a bit misleading. When set, mask registers will be
> updated with regmap_write_bits() instead of regmap_update_bits(),
> but regmap_write_bits() still does a read-modify-write under the
> hood. It's not a write-only operation.
>
> Performing a simple regmap_write() is probably more useful, since
> it can be used for chips that have separate set & clear registers
> for controlling mask bits. Such registers are normally volatile
> and read as 0, so avoiding a register read minimizes bus traffic.

Reading your explanations and the code, I would rather think about
fixing the regmap_write_bits() to be writeonly op.

Otherwise it's unclear what's the difference between
regmap_write_bits() vs. regmap_update_bits().

...

>         if (d->chip->mask_writeonly)
> -               return regmap_write_bits(d->map, reg, mask, val);
> +               return regmap_write(d->map, reg, val & mask);
>         else
>                 return regmap_update_bits(d->map, reg, mask, val);

-- 
With Best Regards,
Andy Shevchenko