linux-kernel - Re: [PATCH v13 2/2] clk: clk-loongson2: add clock controller driver support

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Date:   Tue, 14 Mar 2023 07:49:40 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        kernel test robot <lkp@...el.com>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, zhuyinbo <zhuyinbo@...ngson.cn>
Cc:     oe-kbuild-all@...ts.linux.dev, Jianmin Lv <lvjianmin@...ngson.cn>,
        Liu Peibao <liupeibao@...ngson.cn>, wanghongliang@...ngson.cn,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH v13 2/2] clk: clk-loongson2: add clock controller driver
 support

On 13/03/2023 19:20, Stephen Boyd wrote:
>>>> The CONFIG_64BIT not enabled in your config file, I will add a depend on 
>>>> "CONFIG_64BIT" in my clock driver to fix this compile error.
>>>
>>> Do you need to use readq() here? Can you read two 32-bit registers with
>>> readl() and put them together for a 64-bit number?
>>
>> If the platform supports 64-bit reads and these are actually one
>> register, then readq makes sense - code is more readable, smaller, more
>> efficient.
>>
> 
> Please read the section in Documentation/driver-api/device-io.rst about
> hi_lo_readq() and <linux/io-64-nonatomic-lo-hi.h>. We shouldn't need to
> restrict the driver to CONFIG_64BIT. Instead, include one of these
> header files to get the IO access primitives.

These primitives are for 32bit access. Quoting: "on 32-bit
architectures". What's the point of them if the code *will never* run on
32-bit? It will be a fake choice of linux/io-64-nonatomic-lo-hi.h or
linux/io-64-nonatomic-hi-lo.h misleading users to think this was tested
on 32-bit.

Best regards,
Krzysztof