linux-kernel - [PATCH] x86/mm: Clean up types in xlate_dev_mem

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Message-ID: <20150508105055.GA14063@gmail.com>
Date:	Fri, 8 May 2015 12:50:55 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo2.kernel.org@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] x86/mm: Clean up types in xlate_dev_mem_ptr() some more


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Ugh, I pulled, but:
> 
> On Wed, May 6, 2015 at 5:58 AM, Ingo Molnar <mingo2.kernel.org@...il.com> wrote:
> >
> > Ingo Molnar (1):
> >       x86/mm: Clean up types in xlate_dev_mem_ptr()
> >
> > diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> > index fdf617c00e2f..4bf037b20f47 100644
> > --- a/arch/x86/mm/ioremap.c
> > +++ b/arch/x86/mm/ioremap.c
> > @@ -332,18 +332,20 @@ EXPORT_SYMBOL(iounmap);
> >   */
> >  void *xlate_dev_mem_ptr(phys_addr_t phys)
> >  {
> > +       unsigned long start  = phys &  PAGE_MASK;
> > +       unsigned long offset = phys & ~PAGE_MASK;
> > +       unsigned long vaddr;
> 
> That "unsigned long vaddr" is just stupid and not a cleanup.
> 
> It causes two pointless casts:
> 
> > +       vaddr = (unsigned long)ioremap_cache(start, PAGE_SIZE);
> > +       /* Only add the offset on success and return NULL if the ioremap() failed: */
> > +       if (vaddr)
> > +               vaddr += offset;
> >
> > +       return (void *)vaddr;
> 
> neither of which is helpful in the least. And the "vaddr += offset" 
> would work equally well in "void *", gcc is perfectly happy to treat 
> "void *" arithmetic as byte offsets, it's both documented and 
> already extensively used in the kernel.

Yeah, not sure why I didn't notice that, I love void * arithmetics.

> So the cleanup to use "start/offset" is a good cleanup, but you 
> should have kept "addr" as a pointer.

Something like the patch below?

Thanks,

	Ingo

===================>
>From 562bfca4c80175d1d18eef5c3f4bb8dda53c03e4 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...nel.org>
Date: Fri, 8 May 2015 12:43:53 +0200
Subject: [PATCH] x86/mm: Clean up types in xlate_dev_mem_ptr() some more

So Linus noticed that in:

  94d4b4765b7d ("x86/mm: Clean up types in xlate_dev_mem_ptr()")

... I added two nonsensical casts, due to the poor type choice
for 'vaddr'.

Change it to 'void *' and take advantage of void * arithmetics.

This removes the casts.

( Also remove a nonsensical return line from unxlate_dev_mem_ptr()
  while at it. )

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/mm/ioremap.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 70e7444c6835..27ff21216dfa 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -353,18 +353,18 @@ void *xlate_dev_mem_ptr(phys_addr_t phys)
 {
 	unsigned long start  = phys &  PAGE_MASK;
 	unsigned long offset = phys & ~PAGE_MASK;
-	unsigned long vaddr;
+	void *vaddr;
 
 	/* If page is RAM, we can use __va. Otherwise ioremap and unmap. */
 	if (page_is_ram(start >> PAGE_SHIFT))
 		return __va(phys);
 
-	vaddr = (unsigned long)ioremap_cache(start, PAGE_SIZE);
+	vaddr = ioremap_cache(start, PAGE_SIZE);
 	/* Only add the offset on success and return NULL if the ioremap() failed: */
 	if (vaddr)
 		vaddr += offset;
 
-	return (void *)vaddr;
+	return vaddr;
 }
 
 void unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
@@ -373,7 +373,6 @@ void unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
 		return;
 
 	iounmap((void __iomem *)((unsigned long)addr & PAGE_MASK));
-	return;
 }
 
 static pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)] __page_aligned_bss;
--
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