linux-kernel - Re: drivers/scsi/ncr53c8xx.c:5306:9: sparse: sparse: cast truncates bits from constant value (58f becomes 8f)

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Date:   Fri, 15 May 2020 12:00:26 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     kbuild test robot <lkp@...el.com>
Cc:     Michal Simek <monstr@...str.eu>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Stefan Asserhall <stefan.asserhall@...inx.com>,
        linux-scsi@...r.kernel.org, linux-parisc@...r.kernel.org
Subject: Re: drivers/scsi/ncr53c8xx.c:5306:9: sparse: sparse: cast truncates
 bits from constant value (58f becomes 8f)

On Sat, May 16, 2020 at 02:20:38AM +0800, kbuild test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   051e6b7e34b9bd24f46725f74994a4d3a653966e
> commit: 06e85c7e9a1c1356038936566fc23f7c0d363b96 asm-generic: fix unistd_32.h generation format
> date:   5 weeks ago

I don't see how that commit in any way reflects this error message.

> reproduce:
>         # apt-get install sparse
>         # sparse version: v0.6.1-193-gb8fad4bc-dirty
>         git checkout 06e85c7e9a1c1356038936566fc23f7c0d363b96
>         make ARCH=x86_64 allmodconfig

I can't even see a way to build the ncr53c8xx module with this config.
Unless somebody reenabled EISA on x86, the only way I can see to
still build this driver is on PA-RISC with the ZALON code.

>         make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kbuild test robot <lkp@...el.com>
> 
> 
> sparse warnings: (new ones prefixed by >>)
> 
> >> drivers/scsi/ncr53c8xx.c:5306:9: sparse: sparse: cast truncates bits from constant value (58f becomes 8f)
> 
> ^1da177e4c3f41 Linus Torvalds 2005-04-16 @5306  	OUTW (nc_sien , STO|HTH|MA|SGE|UDC|RST|PAR);

This seems entirely intentional.

Something like this should do the job (whitespace damaged):

+++ b/drivers/scsi/ncr53c8xx.h
@@ -407,7 +407,7 @@
 
 #ifdef CONFIG_SCSI_NCR53C8XX_NO_WORD_TRANSFERS
 /* Only 8 or 32 bit transfers allowed */
-#define OUTW_OFF(o, val)       do { writeb((char)((val) >> 8), (char __iomem *)np->reg + ncr_offw(o)); writeb((char)(val), (char __iomem *)np->reg + ncr_offw(o) + 1); } while (0)
+#define OUTW_OFF(o, val)       do { writeb((char)((val) >> 8), (char __iomem *)np->reg + ncr_offw(o)); writeb((char)((val) & 0xff), (char __iomem *)np->reg + ncr_offw(o) + 1); } while (0)
 #else
 #define OUTW_OFF(o, val)       writew_raw((val), (char __iomem *)np->reg + ncr_offw(o))
 #endif