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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Date:	Tue, 23 Jun 2015 17:40:55 -0700
From:	Joe Perches <joe@...ches.com>
To:	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Cc:	nick <xerofoify@...il.com>, ulf.hansson@...aro.org,
	ben.dooks@...ethink.co.uk, ykaneko0929@...il.com,
	laurent.pinchart+renesas@...asonboard.com,
	kouichi.tomita.yn@...esas.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 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.


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