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 18:54:22 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: Linus Walleij <linus.walleij@...aro.org>, Mark Brown <broonie@...nel.org>
CC: <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 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/

-Mukesh

> 
> Yours,
> Linus Walleij