linux-kernel - Re: [PATCH] ata: pata_cs5535: Fix W=1 warnings

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Date:   Tue, 28 Jun 2022 10:27:19 +0100
From:   John Garry <john.garry@...wei.com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        <s.shtylyov@....ru>
CC:     <linux-ide@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ata: pata_cs5535: Fix W=1 warnings

On 28/06/2022 09:59, Damien Le Moal wrote:
> On 6/27/22 22:12, John Garry wrote:
>> x86_64 allmodconfig build with W=1 gives these warnings:
>>
>> drivers/ata/pata_cs5535.c: In function ‘cs5535_set_piomode’:
>> drivers/ata/pata_cs5535.c:93:11: error: variable ‘dummy’ set but not used [-Werror=unused-but-set-variable]
>>    u32 reg, dummy;
>>             ^~~~~
>> drivers/ata/pata_cs5535.c: In function ‘cs5535_set_dmamode’:
>> drivers/ata/pata_cs5535.c:132:11: error: variable ‘dummy’ set but not used [-Werror=unused-but-set-variable]
>>    u32 reg, dummy;
>>             ^~~~~
>> cc1: all warnings being treated as errors
>>
>> Mark variables 'dummy' as "maybe unused" to satisfy when rdmsr() is
>> stubbed, which is the same as what we already do in pata_cs5536.c .
>>
>> Signed-off-by: John Garry <john.garry@...wei.com>
> 
> Looks good, but I wonder why I am not getting this warning. I always do
> W=1 and C=1 builds. I tried allmodconfig now and I am not getting the
> warning...

eh, I'm not sure why. It's the only driver in drivers/ata/ which gives 
such a problem.

I'm using gcc 9:
gcc version 9.3.1 20200406 [revision 
6db837a5288ee3ca5ec504fbd5a765817e556ac2] (SUSE Linux)

Then I cross-compiled from my arm64 machine (to x86) and still got it:
john@...ntu:~/kernel-dev$ /usr/bin/x86_64-linux-gnu-gcc --version
x86_64-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0

> 
>>
>> diff --git a/drivers/ata/pata_cs5535.c b/drivers/ata/pata_cs5535.c
>> index 6725931f3c35..c2c3238ff84b 100644
>> --- a/drivers/ata/pata_cs5535.c
>> +++ b/drivers/ata/pata_cs5535.c
>> @@ -90,7 +90,7 @@ static void cs5535_set_piomode(struct ata_port *ap, struct ata_device *adev)
>>   	static const u16 pio_cmd_timings[5] = {
>>   		0xF7F4, 0x53F3, 0x13F1, 0x5131, 0x1131
>>   	};
>> -	u32 reg, dummy;
>> +	u32 reg, __maybe_unused dummy;
>>   	struct ata_device *pair = ata_dev_pair(adev);
>>   
>>   	int mode = adev->pio_mode - XFER_PIO_0;
>> @@ -129,7 +129,7 @@ static void cs5535_set_dmamode(struct ata_port *ap, struct ata_device *adev)
>>   	static const u32 mwdma_timings[3] = {
>>   		0x7F0FFFF3, 0x7F035352, 0x7F024241
>>   	};
>> -	u32 reg, dummy;
>> +	u32 reg, __maybe_unused dummy;
>>   	int mode = adev->dma_mode;
>>   
>>   	rdmsr(ATAC_CH0D0_DMA + 2 * adev->devno, reg, dummy);
> 
>