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

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Date:   Mon, 17 May 2021 09:39:45 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Dmitry Osipenko <digetx@...il.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

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. 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.


Best regards,
Krzysztof