linux-kernel - RE: [PATCH] 6fire: Convert byte_rev

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Date:	Wed, 29 Oct 2014 10:42:00 +0800
From:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>
To:	'Joe Perches' <joe@...ches.com>, Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.de>
CC:	Russell King <linux@....linux.org.uk>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Will Deacon <Will.Deacon@....com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	alsa-devel <alsa-devel@...a-project.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Will Deacon <Will.Deacon@....com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	alsa-devel <alsa-devel@...a-project.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] 6fire: Convert byte_rev_table uses to bitrev8

> Use the inline function instead of directly indexing the array.
> 
> This allows some architectures with hardware instructions for bit reversals
> to eliminate the array.
> 
> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
> On Sun, 2014-10-26 at 23:46 -0700, Joe Perches wrote:
> > On Mon, 2014-10-27 at 14:37 +0800, Wang, Yalin wrote:
> > > this change add CONFIG_HAVE_ARCH_BITREVERSE config option, so that
> > > we can use arm/arm64 rbit instruction to do bitrev operation by
> > > hardware.
> []
> > > diff --git a/include/linux/bitrev.h b/include/linux/bitrev.h index
> > > 7ffe03f..ef5b2bb 100644
> > > --- a/include/linux/bitrev.h
> > > +++ b/include/linux/bitrev.h
> > > @@ -3,6 +3,14 @@
> > >
> > >  #include <linux/types.h>
> > >
> > > +#ifdef CONFIG_HAVE_ARCH_BITREVERSE
> > > +#include <asm/bitrev.h>
> > > +
> > > +#define bitrev32 __arch_bitrev32
> > > +#define bitrev16 __arch_bitrev16
> > > +#define bitrev8 __arch_bitrev8
> > > +
> > > +#else
> > >  extern u8 const byte_rev_table[256];
> 
>  sound/usb/6fire/firmware.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/usb/6fire/firmware.c b/sound/usb/6fire/firmware.c index
> 3b02e54..62c25e7 100644
> --- a/sound/usb/6fire/firmware.c
> +++ b/sound/usb/6fire/firmware.c
> @@ -316,7 +316,7 @@ static int usb6fire_fw_fpga_upload(
> 
>  	while (c != end) {
>  		for (i = 0; c != end && i < FPGA_BUFSIZE; i++, c++)
> -			buffer[i] = byte_rev_table[(u8) *c];
> +			buffer[i] = bitrev8((u8)*c);
> 
>  		ret = usb6fire_fw_fpga_write(device, buffer, i);
>  		if (ret < 0) {
> 
I think the most safe way is change byte_rev_table[] to be satic,
So that no driver can access it directly,
The build error can remind the developer if they use byte_rev_table[]
Directly .

Thanks
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