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

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Date:   Mon, 13 Mar 2023 11:20:10 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Krzysztof Kozlowski <krzk@...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

Quoting Krzysztof Kozlowski (2023-03-10 00:42:47)
> On 10/03/2023 00:47, Stephen Boyd wrote:
> > Quoting zhuyinbo (2023-03-08 18:58:02)
> >>
> >> 在 2023/3/8 下午8:16, kernel test robot 写道:
> >>> Hi Yinbo,
> >>>
> > [...]
> >>>
> >>>     drivers/clk/clk-loongson2.c: In function 'loongson2_calc_pll_rate':
> >>>>> drivers/clk/clk-loongson2.c:79:15: error: implicit declaration of function 'readq'; did you mean 'readl'? [-Werror=implicit-function-declaration]
> >>>        79 |         val = readq(loongson2_pll_base + offset);
> >>>           |               ^~~~~
> >>>           |               readl
> >>>     cc1: some warnings being treated as errors
> >>
> >> 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.