linux-kernel - Re: [PATCH] dma: bcm2835: Fix compiler warning on arm64.

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Date:	Mon, 06 Jun 2016 10:15:05 -0700
From:	Eric Anholt <eric@...olt.net>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dotorg.org>,
	Lee Jones <lee@...nel.org>, dmaengine@...r.kernel.org
Subject: Re: [PATCH] dma: bcm2835: Fix compiler warning on arm64.

Vinod Koul <vinod.koul@...el.com> writes:

> On Fri, Jun 03, 2016 at 07:23:33PM -0700, Eric Anholt wrote:
>> The min() macro was complaining about mismatched types.  The max len
>> is at most SZ_1G, so we can just put it in an unsigned int.
>> 
>> Signed-off-by: Eric Anholt <eric@...olt.net>
>> ---
>> 
>> Vinod, if you ack it, this one would be nice to be able to merge
>> through the -soc tree, so that when we enable of arm64 builds of this
>> driver we don't introduce a new compiler warning.
>> 
>>  drivers/dma/bcm2835-dma.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
>> index 6149b27c33ad..1fa11fc067c6 100644
>> --- a/drivers/dma/bcm2835-dma.c
>> +++ b/drivers/dma/bcm2835-dma.c
>> @@ -393,7 +393,7 @@ static void bcm2835_dma_fill_cb_chain_with_sg(
>>  	unsigned int sg_len)
>>  {
>>  	struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
>> -	size_t max_len = bcm2835_dma_max_frame_length(c);
>> +	unsigned int max_len = bcm2835_dma_max_frame_length(c);
>
> bcm2835_dma_max_frame_length() returns size_t. so this should also add a
> complain about type mismatch as well!
>
> Also, wouldn't it be better to make both args of min()  as size_t then?

Assignments from different sizes don't produce warnings.  The other arg
of the min() is a u32, and this value is known to be < u32, so I don't
see the problem.  I could start promoting u32s to size_ts instead, but I
don't know where that would end.

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