[pcnet32] Eliminate redundant register read

The value of ( ( x & 0x0c00 ) | 0x0c00 ) is always 0x0c00 regardless of the value of x, and so the read_csr() is redundant. (There are no read side effects for this register, according to the datasheet.) This line of code originated in Linux kernel 2.3.19pre1 as a->write_csr(ioaddr, 80, a->read_csr(ioaddr, 80) | 0x0c00); and was modified in kernel 2.3.41pre4 to read a->write_csr(ioaddr, 80, (a->read_csr(ioaddr, 80) & 0x0C00) | 0x0c00); In the absence of commit messages, the intention of the code is unclear. However, the logic resulting in a fixed value of 0x0c00 has remained unaltered for over 17 years, and can probably be assumed to have the correct overall result. Signed-off-by: Michael Brown <mcb30@ipxe.org>
ipxe · Mar 23, 2017 · 19d3e96 · 19d3e96
1 parent 1ff1eeb
commit 19d3e96
Showing 1 changed file with 1 addition and 2 deletions.
diff --git a/src/drivers/net/pcnet32.c b/src/drivers/net/pcnet32.c
@@ -414,8 +414,7 @@ pcnet32_chip_detect ( struct pcnet32_private *priv )
 	if (fset) {
 		a->write_bcr ( ioaddr, 18,
 			( a->read_bcr ( ioaddr, 18 ) | 0x0860 ) );
-		a->write_csr ( ioaddr, 80,
-			( a->read_csr ( ioaddr, 80 ) & 0x0C00) | 0x0C00 );
+		a->write_csr ( ioaddr, 80, 0x0c00 );
 	}
 
 	priv->full_duplex = fdx;