[RFC] bmac:change to use bitrev8() generic function

Subsystems: networking drivers, the rest

5 messages, 3 authors, 2015-08-11 · open the first message on its own page

[RFC] bmac:change to use bitrev8() generic function

From: yalin wang <hidden>
Date: 2015-08-10 10:10:20

This change to use generic bitrev8() for bmac driver.

Signed-off-by: yalin wang <redacted>
---
 drivers/net/ethernet/apple/bmac.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/apple/bmac.c b/drivers/net/ethernet/apple/bmac.c
index a65d7a6..e749747 100644
--- a/drivers/net/ethernet/apple/bmac.c
+++ b/drivers/net/ethernet/apple/bmac.c

@@ -22,6 +22,7 @@
 #include <linux/bitrev.h>
 #include <linux/ethtool.h>
 #include <linux/slab.h>
+#include <linux/bitrev.h>
 #include <asm/prom.h>
 #include <asm/dbdma.h>
 #include <asm/io.h>

@@ -805,18 +806,6 @@ static irqreturn_t bmac_txdma_intr(int irq, void *dev_id)
 }
 
 #ifndef SUNHME_MULTICAST
-/* Real fast bit-reversal algorithm, 6-bit values */
-static int reverse6[64] = {
-	0x0,0x20,0x10,0x30,0x8,0x28,0x18,0x38,
-	0x4,0x24,0x14,0x34,0xc,0x2c,0x1c,0x3c,
-	0x2,0x22,0x12,0x32,0xa,0x2a,0x1a,0x3a,
-	0x6,0x26,0x16,0x36,0xe,0x2e,0x1e,0x3e,
-	0x1,0x21,0x11,0x31,0x9,0x29,0x19,0x39,
-	0x5,0x25,0x15,0x35,0xd,0x2d,0x1d,0x3d,
-	0x3,0x23,0x13,0x33,0xb,0x2b,0x1b,0x3b,
-	0x7,0x27,0x17,0x37,0xf,0x2f,0x1f,0x3f
-};
-
 static unsigned int
 crc416(unsigned int curval, unsigned short nxtval)
 {

@@ -871,7 +860,7 @@ bmac_addhash(struct bmac_data *bp, unsigned char *addr)
 
 	if (!(*addr)) return;
 	crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */
-	crc = reverse6[crc];	/* Hyperfast bit-reversing algorithm */
+	crc = bitrev8((u8)crc);
 	if (bp->hash_use_count[crc]++) return; /* This bit is already set */
 	mask = crc % 16;
 	mask = (unsigned char)1 << mask;

@@ -886,7 +875,7 @@ bmac_removehash(struct bmac_data *bp, unsigned char *addr)
 
 	/* Now, delete the address from the filter copy, as indicated */
 	crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */
-	crc = reverse6[crc];	/* Hyperfast bit-reversing algorithm */
+	crc = bitrev8((u8)crc);
 	if (bp->hash_use_count[crc] == 0) return; /* That bit wasn't in use! */
 	if (--bp->hash_use_count[crc]) return; /* That bit is still in use */
 	mask = crc % 16;

-- 
1.9.1

Re: [RFC] bmac:change to use bitrev8() generic function

From: Tobias Klauser <tklauser@distanz.ch>
Date: 2015-08-10 11:49:10

On 2015-08-10 at 11:53:41 +0200, yalin wang [off-list ref] wrote:

quoted hunk

This change to use generic bitrev8() for bmac driver.

Signed-off-by: yalin wang <redacted>
---
 drivers/net/ethernet/apple/bmac.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/apple/bmac.c b/drivers/net/ethernet/apple/bmac.c
index a65d7a6..e749747 100644
--- a/drivers/net/ethernet/apple/bmac.c
+++ b/drivers/net/ethernet/apple/bmac.c

@@ -22,6 +22,7 @@
 #include <linux/bitrev.h>
 #include <linux/ethtool.h>
 #include <linux/slab.h>
+#include <linux/bitrev.h>
 #include <asm/prom.h>
 #include <asm/dbdma.h>
 #include <asm/io.h>

@@ -805,18 +806,6 @@ static irqreturn_t bmac_txdma_intr(int irq, void *dev_id)
 }
 
 #ifndef SUNHME_MULTICAST
-/* Real fast bit-reversal algorithm, 6-bit values */
-static int reverse6[64] = {
-	0x0,0x20,0x10,0x30,0x8,0x28,0x18,0x38,
-	0x4,0x24,0x14,0x34,0xc,0x2c,0x1c,0x3c,
-	0x2,0x22,0x12,0x32,0xa,0x2a,0x1a,0x3a,
-	0x6,0x26,0x16,0x36,0xe,0x2e,0x1e,0x3e,
-	0x1,0x21,0x11,0x31,0x9,0x29,0x19,0x39,
-	0x5,0x25,0x15,0x35,0xd,0x2d,0x1d,0x3d,
-	0x3,0x23,0x13,0x33,0xb,0x2b,0x1b,0x3b,
-	0x7,0x27,0x17,0x37,0xf,0x2f,0x1f,0x3f
-};
-
 static unsigned int
 crc416(unsigned int curval, unsigned short nxtval)
 {

@@ -871,7 +860,7 @@ bmac_addhash(struct bmac_data *bp, unsigned char *addr)
 
 	if (!(*addr)) return;
 	crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */
-	crc = reverse6[crc];	/* Hyperfast bit-reversing algorithm */
+	crc = bitrev8((u8)crc);

No, this won't work. reverse6 works on 6 bit values, while bitrev8 works
on 8bit values, e.g. reverse6[1] = 0x20, while bitrev8(1) = 0x80

RE: [RFC] bmac:change to use bitrev8() generic function

From: David Laight <hidden>
Date: 2015-08-10 12:05:12

From: Tobias Klauser
Sent: 10 August 2015 12:49
On 2015-08-10 at 11:53:41 +0200, yalin wang [off-list ref] wrote:

quoted

This change to use generic bitrev8() for bmac driver.

...

quoted

@@ -871,7 +860,7 @@ bmac_addhash(struct bmac_data *bp, unsigned char *addr)

 	if (!(*addr)) return;
 	crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */

Why not *((u8 *)addr + 1) & 0x3f

quoted

-	crc = reverse6[crc];	/* Hyperfast bit-reversing algorithm */
+	crc = bitrev8((u8)crc);

No, this won't work. reverse6 works on 6 bit values, while bitrev8 works
on 8bit values, e.g. reverse6[1] = 0x20, while bitrev8(1) = 0x80

You could use bitrev8(n) >> 2.

But that is a 'strange' map of a 7-bit value to a 6-bit one.

I thought it was more common for ethernet hardware to use the
value of the crc register after all 6 bytes of the mac address
had been processed.

	David

Re: [RFC] bmac:change to use bitrev8() generic function

From: yalin wang <hidden>
Date: 2015-08-11 02:06:30

On Aug 10, 2015, at 20:02, David Laight [off-list ref] wrote:

quoted

From: Tobias Klauser
Sent: 10 August 2015 12:49
On 2015-08-10 at 11:53:41 +0200, yalin wang [off-list ref] wrote:

quoted

This change to use generic bitrev8() for bmac driver.

...

quoted

@@ -871,7 +860,7 @@ bmac_addhash(struct bmac_data *bp, unsigned char *addr)

	if (!(*addr)) return;
	crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */

Why not *((u8 *)addr + 1) & 0x3f

quoted

-	crc = reverse6[crc];	/* Hyperfast bit-reversing algorithm */
+	crc = bitrev8((u8)crc);

No, this won't work. reverse6 works on 6 bit values, while bitrev8 works
on 8bit values, e.g. reverse6[1] = 0x20, while bitrev8(1) = 0x80

You could use bitrev8(n) >> 2.

But that is a 'strange' map of a 7-bit value to a 6-bit one.

I thought it was more common for ethernet hardware to use the
value of the crc register after all 6 bytes of the mac address
had been processed.

oh, my mistake, i will change it in V2 for review.

[RFC V2] bmac:change to use bitrev8() generic function

From: yalin wang <hidden>
Date: 2015-08-11 02:28:25

This change to use generic bitrev8() for bmac driver.

Signed-off-by: yalin wang <redacted>
---
 drivers/net/ethernet/apple/bmac.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/apple/bmac.c b/drivers/net/ethernet/apple/bmac.c
index a65d7a6..7f7a398 100644
--- a/drivers/net/ethernet/apple/bmac.c
+++ b/drivers/net/ethernet/apple/bmac.c

@@ -22,6 +22,7 @@
 #include <linux/bitrev.h>
 #include <linux/ethtool.h>
 #include <linux/slab.h>
+#include <linux/bitrev.h>
 #include <asm/prom.h>
 #include <asm/dbdma.h>
 #include <asm/io.h>

@@ -805,18 +806,6 @@ static irqreturn_t bmac_txdma_intr(int irq, void *dev_id)
 }
 
 #ifndef SUNHME_MULTICAST
-/* Real fast bit-reversal algorithm, 6-bit values */
-static int reverse6[64] = {
-	0x0,0x20,0x10,0x30,0x8,0x28,0x18,0x38,
-	0x4,0x24,0x14,0x34,0xc,0x2c,0x1c,0x3c,
-	0x2,0x22,0x12,0x32,0xa,0x2a,0x1a,0x3a,
-	0x6,0x26,0x16,0x36,0xe,0x2e,0x1e,0x3e,
-	0x1,0x21,0x11,0x31,0x9,0x29,0x19,0x39,
-	0x5,0x25,0x15,0x35,0xd,0x2d,0x1d,0x3d,
-	0x3,0x23,0x13,0x33,0xb,0x2b,0x1b,0x3b,
-	0x7,0x27,0x17,0x37,0xf,0x2f,0x1f,0x3f
-};
-
 static unsigned int
 crc416(unsigned int curval, unsigned short nxtval)
 {

@@ -871,7 +860,7 @@ bmac_addhash(struct bmac_data *bp, unsigned char *addr)
 
 	if (!(*addr)) return;
 	crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */
-	crc = reverse6[crc];	/* Hyperfast bit-reversing algorithm */
+	crc = bitrev8((u8)crc) >> 2;
 	if (bp->hash_use_count[crc]++) return; /* This bit is already set */
 	mask = crc % 16;
 	mask = (unsigned char)1 << mask;

@@ -886,7 +875,7 @@ bmac_removehash(struct bmac_data *bp, unsigned char *addr)
 
 	/* Now, delete the address from the filter copy, as indicated */
 	crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */
-	crc = reverse6[crc];	/* Hyperfast bit-reversing algorithm */
+	crc = bitrev8((u8)crc) >> 2;
 	if (bp->hash_use_count[crc] == 0) return; /* That bit wasn't in use! */
 	if (--bp->hash_use_count[crc]) return; /* That bit is still in use */
 	mask = crc % 16;

-- 
1.9.1

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