linux-kernel - Re: [PATCH v11 1/4] firmware: qcom: scm: provide a read-modify-write function

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Date: Tue, 9 Jan 2024 14:34:10 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Mukesh Ojha <quic_mojha@...cinc.com>
Cc: Mark Brown <broonie@...nel.org>, andersson@...nel.org, konrad.dybcio@...aro.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-gpio@...r.kernel.org
Subject: Re: [PATCH v11 1/4] firmware: qcom: scm: provide a read-modify-write function

On Tue, Jan 9, 2024 at 2:24 PM Mukesh Ojha <quic_mojha@...cinc.com> wrote:
> On 1/9/2024 6:44 PM, Linus Walleij wrote:
> > On Mon, Jan 8, 2024 at 4:28 PM Mukesh Ojha <quic_mojha@...cinc.com> wrote:
> >
> >> It was realized by Srinivas K. that there is a need of
> >> read-modify-write scm exported function so that it can
> >> be used by multiple clients.
> >>
> >> Let's introduce qcom_scm_io_rmw() which masks out the bits
> >> and write the passed value to that bit-offset.
> > (...)
> >> +int qcom_scm_io_rmw(phys_addr_t addr, unsigned int mask, unsigned int val)
> >> +{
> >> +       unsigned int old, new;
> >> +       int ret;
> >> +
> >> +       if (!__scm)
> >> +               return -EINVAL;
> >> +
> >> +       spin_lock(&__scm->lock);
> >> +       ret = qcom_scm_io_readl(addr, &old);
> >> +       if (ret)
> >> +               goto unlock;
> >> +
> >> +       new = (old & ~mask) | (val & mask);
> >> +
> >> +       ret = qcom_scm_io_writel(addr, new);
> >> +unlock:
> >> +       spin_unlock(&__scm->lock);
> >> +       return ret;
> >> +}
> >> +EXPORT_SYMBOL_GPL(qcom_scm_io_rmw);
> >
> > This looks a lot like you are starting to re-invent regmaps
> > regmap_update_bits().
> >
> > If you are starting to realize you need more and more of
> > regmap, why not use regmap and its functions?
>
> I think, this discussion has happened already ..
>
> https://lore.kernel.org/lkml/CACRpkdb95V5GC81w8fiuLfx_V1DtWYpO33FOfMnArpJeC9SDQA@mail.gmail.com/

That discussion ended with:

[Bjorn]
> We'd still need qcom_scm_io_readl() and qcom_scm_io_writel() exported to
> implement the new custom regmap implementation - and the struct
> regmap_config needed in just pinctrl-msm alone would be larger than the
> one function it replaces.

When you add more and more accessors the premise starts to
change, and it becomes more and more of a reimplementation.

It may be time to actually fix this.

Yours,
Linus Walleij