linux-kernel - Re: [PATCHv2] mmc:Add pointer cast to uintptr_t for slave_id_rx and tx in the function, sh_mmcif_request_dma

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Message-ID: <1435107273.2504.43.camel@perches.com>
Date:	Tue, 23 Jun 2015 17:54:33 -0700
From:	Joe Perches <joe@...ches.com>
To:	nick <xerofoify@...il.com>
Cc:	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	ulf.hansson@...aro.org, ben.dooks@...ethink.co.uk,
	ykaneko0929@...il.com, laurent.pinchart+renesas@...asonboard.com,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] mmc:Add pointer cast to uintptr_t for slave_id_rx and
 tx in the function, sh_mmcif_request_dma_one

On Tue, 2015-06-23 at 20:44 -0400, nick wrote:
> 
> On 2015-06-23 08:40 PM, Joe Perches wrote:
> > On Wed, 2015-06-24 at 00:24 +0000, Kuninori Morimoto wrote:
> >> Hi Joe, Nick
> >>
> >>>>>> This adds a cast to the variables,slave_id_rx and slave_id_rx
> >>>>>> to uintptr_t before casting to void* in order to avoid build
> >>>>>> warning on 64bit platforms for the function, sh_mmcif_request_dma_one.
> >>>> []
> >>>>>> diff --git a/drivers/mmc/host/sh_mmcif.c b/drivers/mmc/host/sh_mmcif.c
> >>>> []
> >>>>>> @@ -398,8 +398,8 @@ sh_mmcif_request_dma_one(struct sh_mmcif_host *host,
> >>>>>>  
> >>>>>>  	if (pdata)
> >>>>>>  		slave_data = direction == DMA_MEM_TO_DEV ?
> >>>>>> -			(void *)pdata->slave_id_tx :
> >>>>>> -			(void *)pdata->slave_id_rx;
> >>>>>> +			(void *)(uintptr_t)pdata->slave_id_tx :
> >>>>>> +			(void *)(uintptr_t)pdata->slave_id_rx;
> >>>>
> >>>> It's far more common (~10:1) in the kernel to cast using
> >>>> 	(<type> *)(unsigned long)<foo>
> >>>> than
> >>>> 	(<type> *)(uintptr_t)<foo>
> >>>>
> >>> Joe,
> >>> I agree it's more common in the kernel but one of the maintainers when I sent
> >>> this patch a month ago requested I use uintpr_t instead of unsigned long for
> >>> the casting. Otherwise I would have done the cast to fix the build warning
> >>> with unsigned long instead.
> >>
> >> This mail
> >> http://thread.gmane.org/gmane.linux.kernel.mmc/32304
> > 
> > uintptr_t was introduced to avoid ptrdiff_t misuse in
> > commit 142956af5250 ("fix abuses of ptrdiff_t") by Al Viro.
> > 
> > unsigned long is preponderant, long is used about 1/4 as
> > often as unsigned long, uintptr_t is relatively uncommon.
> > 
> > If someone wants to go and convert the 800 or so casts to
> > long or unsigned long to uintptr_t so that's the style most
> > frequently used, that'd be different.  I'm not going to
> > submit any patches for that.
> > 
> > 
> I am not disagreeing it was just easier to listen to the maintainer rather
> then get in a technical argument over which type is better for the cast.

Ulf Hansson is the maintainer.

Laurent has authored a couple patches to that file and he gave
you his opinion about using uintptr_t.

I'm giving an opinion too, just with a little statistics.

I think it's better to use the style that the kernel generally
uses.

I'll stop replying now.


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