linux-kernel - Re: [PATCH v2 3/4] memory: tegra124-emc: Fix compilation warnings on 64bit platforms

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Message-ID: <c120ecf5-7202-9f1d-6e70-a99db2f5335f@gmail.com>
Date:   Mon, 17 May 2021 16:47:37 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Mikko Perttunen <mperttunen@...dia.com>
Cc:     linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v2 3/4] memory: tegra124-emc: Fix compilation warnings on
 64bit platforms

17.05.2021 16:39, Krzysztof Kozlowski пишет:
> On 17/05/2021 09:35, Dmitry Osipenko wrote:
>> 17.05.2021 14:28, Krzysztof Kozlowski пишет:
>>> On 16/05/2021 12:12, Dmitry Osipenko wrote:
>>>> Fix compilation warning on 64bit platforms caused by implicit promotion
>>>> of 32bit signed integer to a 64bit unsigned value which happens after
>>>> enabling compile-testing of the driver.
>>>>
>>>> Suggested-by: Nathan Chancellor <nathan@...nel.org>
>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>> ---
>>>>  drivers/memory/tegra/tegra124-emc.c | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/memory/tegra/tegra124-emc.c b/drivers/memory/tegra/tegra124-emc.c
>>>> index 5699d909abc2..c9eb948cf4df 100644
>>>> --- a/drivers/memory/tegra/tegra124-emc.c
>>>> +++ b/drivers/memory/tegra/tegra124-emc.c
>>>> @@ -272,8 +272,8 @@
>>>>  #define EMC_PUTERM_ADJ				0x574
>>>>  
>>>>  #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.

> 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.