[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>

diff --git a/src/drivers/net/pcnet32.c b/src/drivers/net/pcnet32.c
index 26633a248f33b1dcb606db6fb4d0798c3fd693e1..2635aaca224f53b248634f98477ab3b1d3301a02 100644 (file)
--- 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;