linux-kernel - Re: [PATCH 2/2][RFC] mmc: cast unsigned int to typeof(sector

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Message-ID: <87iod756em.wl%kuninori.morimoto.gx@renesas.com>
Date:	Wed, 8 Apr 2015 09:14:46 +0000
From:	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To:	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
CC:	Ulf Hansson <ulf.hansson@...aro.org>,
	<ryusuke.sakato.bx@...esas.com>,
	<yoshihiro.shimoda.uh@...esas.com>,
	<hiroyuki.yokoyama.vx@...esas.com>,
	<takeshi.kihara.df@...esas.com>,
	"Jaehoon Chung" <jh80.chung@...sung.com>,
	Chris Ball <chris@...ntf.net>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	"Grégory Soutadé" <gsoutade@...tion.com>,
	<linux-kernel@...r.kernel.org>, <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH 2/2][RFC] mmc: cast unsigned int to typeof(sector_t) to avoid unexpected error

Hi

> card->csd.capacity is defined as "unsigned int",
> and, sector_t is defined as "u64" or "unsigned long" (depends on CONFIG_LBDAF)
> sector_t data might have strange data if first bit of unsigned int
> was 1. this patch cast it to typeof(sector_t)
> 
> ex) if sector_t was u64
> 
>         unsigned int data;
>         sector_t sector;
> 
>         data = 0x80000000;
>         sector = (data << 8); // 0xffffff8000000000
>         sector = (((typeof(sector_t))data) << 8); // 0x8000000000

Sorry, I noticed this explain (= number of 0) was wrong
Maybe it should be

         data = 0x800000;
         sector = (data << 8); // 0xffffffff80000000
         sector = (((typeof(sector_t))data) << 8); // 0x80000000

or

         data = 0x80000000;
         sector = (data << 8); // 0x0
         sector = (((typeof(sector_t))data) << 8); // 0x8000000000
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