linux-kernel - Re: [PATCH v9 4/4] clk: meson: add sub MMC clock controller driver

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Date:   Mon, 17 Jan 2022 14:24:28 +0800
From:   Liang Yang <liang.yang@...ogic.com>
To:     Stephen Boyd <sboyd@...nel.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Rob Herring <robh+dt@...nel.org>, <linux-clk@...r.kernel.org>
CC:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Victor Wan <victor.wan@...ogic.com>,
        XianWei Zhao <xianwei.zhao@...ogic.com>,
        Kelvin Zhang <kelvin.zhang@...ogic.com>,
        BiChao Zheng <bichao.zheng@...ogic.com>,
        YongHui Yu <yonghui.yu@...ogic.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 4/4] clk: meson: add sub MMC clock controller driver



On 2022/1/15 7:01, Stephen Boyd wrote:
> [ EXTERNAL EMAIL ]
> 
> Quoting Liang Yang (2022-01-13 21:14:46)
>> On 2022/1/14 5:35, Stephen Boyd wrote:
>>> Quoting Liang Yang (2022-01-13 03:57:45)
>>>> diff --git a/drivers/clk/meson/mmc-clkc.c b/drivers/clk/meson/mmc-clkc.c
>>>> new file mode 100644
>>>> index 000000000000..f53977f61390
>>>> --- /dev/null
>>>> +++ b/drivers/clk/meson/mmc-clkc.c
>>>> @@ -0,0 +1,300 @@
> [..]
>>>> +
>>>> +static int mmc_clkc_probe(struct platform_device *pdev)
>>>> +{
>>>> +       struct clk_hw_onecell_data *onecell_data;
>>>> +       struct device *dev = &pdev->dev;
>>>> +       struct mmc_clkc_data *data;
>>>> +       struct regmap *map;
>>>> +       struct clk_regmap *clk, *core;
>>>> +       struct meson_sclk_div_data *div_data;
>>>> +
>>>> +       /*cast to drop the const in match->data*/
>>>
>>> Space after *, also why do we need to cast away const? The user of this
>>> pointer passes it all the way down to mmc_clkc_register_clk() which
>>> could take the data as const void pointer and decide to cast away const
>>> there.
>>
>> if use 'const' here, it  will report a warning:
>> drivers/clk/meson/mmc-clkc.c:224:7: error: assignment discards ‘const’
>> qualifier from pointer targe
>> t type [-Werror=discarded-qualifiers]
>>
>>     data = (const struct mmc_clkc_data *)of_device_get_match_data(dev);
> 
> Of course. The type declaration up above needs const added to it.The parm of mmc_clkc_register_clk_with_parent(...., void *data) does not 
have 'const', so make the type declaration cause a further 'const' cast 
warning. Could i copy these infos just like below:

struct mmc_clkc_data *data_clkc;
......
data = of_device_get_match_data(dev);
data_clkc = devm_kmalloc(dev, sizeof(*data_clkc), GFP_KERNEL);
memcpy(data_clkc, data, sizeof(*data_clkc));
......
clk = mmc_clkc_register_clk_with_parent(...., &data_clkc->rx);

> 
> .