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Subject: Re: [PATCH v2 3/4] memory: tegra124-emc: Fix compilation warnings on
 64bit platforms
To:     Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Mikko Perttunen <mperttunen@nvidia.com>
Cc:     linux-kernel@vger.kernel.org, linux-tegra@vger.kernel.org,
        linux-clk@vger.kernel.org
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From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <9c2b7fe8-551f-288d-eeab-37810aa3f6ba@gmail.com>
Date:   Mon, 17 May 2021 17:23:38 +0300
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17.05.2021 17:04, Krzysztof Kozlowski пишет:
> On 17/05/2021 09:47, Dmitry Osipenko wrote:
>> 17.05.2021 16:39, Krzysztof Kozlowski пишет:
>>>>>>  #define DRAM_DEV_SEL_ALL			0
>>>>>> -#define DRAM_DEV_SEL_0				(2 << 30)
>>>>>> -#define DRAM_DEV_SEL_1				(1 << 30)
>>>>>> +#define DRAM_DEV_SEL_0				(2u << 30)
>>>>>> +#define DRAM_DEV_SEL_1				(1u << 30)
>>>>>
>>>>> Why not using BIT()? This would make even this 2<<30 less awkard...
>>>>
>>>> The bitfield 31:30 is a enum, 3 is a wrong value. Formally it's
>>>> incorrect to use the BIT() macro here.
>>>
>>> Why "3"? BIT(31) is the same as 2<<30.
>>
>> By 3 I meant BIT(31)|BIT(30). This bitfield is explicitly designated as
>> a enum in the hardware documentation.
> 
> I understand it and using BIT() here does not mean someone has to set
> both of them. BIT() is a helper pointing out that you want to toggle one
> bit. It does not mean that it is allowed to do so always!
> 
>>
>>> It's common to use BIT for
>>> register fields which do not accept all possible values. Now you
>>> basically reimplement BIT() which is error-prone.
>>
>> Could you please show couple examples? The common practice today is to
>> use FIELD_PREP helpers, but this driver was written before these helpers
>> existed.
> 
> 
> There are plenty of such examples so I guess it would be easier to ask
> you to provide counter ones. Few IT for enum-like registers found within 2 minutes:
> 
> https://elixir.bootlin.com/linux/latest/C/ident/MAX77620_CNFG_GPIO_INT_MASK
> https://elixir.bootlin.com/linux/v5.13-rc2/source/drivers/regulator/max77650-regulator.c#L18
> https://elixir.bootlin.com/linux/v5.13-rc2/source/drivers/regulator/tps6524x-regulator.c#L62
> https://elixir.bootlin.com/linux/v5.13-rc2/source/drivers/regulator/tps80031-regulator.c#L39
> https://elixir.bootlin.com/linux/v5.13-rc2/source/drivers/regulator/da9121-regulator.h#L200
> https://elixir.bootlin.com/linux/v5.13-rc2/source/drivers/regulator/da9121-regulator.h#L231

Alright, I'll use the BIT macro in the v3.

I also realized now that the tegra30-emc drivers needs the same change.

Thank you for the review.