linux-kernel - Re: [PATCH v2 1/1] x86/early_printk: Use _

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Date:	Sun, 11 Oct 2015 21:18:21 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH v2 1/1] x86/early_printk: Use __iomem address space for
 IO

Andy,

On Fri, 9 Oct 2015, Andy Shevchenko wrote:
>  #ifdef CONFIG_PCI
>  static void mem32_serial_out(unsigned long addr, int offset, int value)
>  {
> -	u32 *vaddr = (u32 *)addr;
> +	void __iomem *vaddr = (void __iomem *)addr;
>  	/* shift implied by pointer type */
>  	writel(value, vaddr + offset);

This is broken. Assume vaddr = 0x1000 and offset = 1

==>  u32 *vaddr = 0x1000;
==>  vaddr + offset = 0x1004

with your change

==>  void __iomem *vaddr = 0x1000;

==>  vaddr + offset = 0x1001

This comment is there for a reason:
>  	/* shift implied by pointer type */

Thanks,

	tglx
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