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| author | Michael Brown | 2017-03-23 16:35:10 +0100 |
|---|---|---|
| committer | Michael Brown | 2017-03-23 16:43:13 +0100 |
| commit | 19d3e966d9ee535fc89e8fa26737cc133882ae1c (patch) | |
| tree | efc66e0d9fc2cb1d10f888e952224d770bf0d747 /src/drivers/net | |
| parent | [golan] Bug fixes and improved paging allocation method (diff) | |
| download | ipxe-19d3e966d9ee535fc89e8fa26737cc133882ae1c.tar.gz ipxe-19d3e966d9ee535fc89e8fa26737cc133882ae1c.tar.xz ipxe-19d3e966d9ee535fc89e8fa26737cc133882ae1c.zip | |
[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>
Diffstat (limited to 'src/drivers/net')
| -rw-r--r-- | src/drivers/net/pcnet32.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/src/drivers/net/pcnet32.c b/src/drivers/net/pcnet32.c index 26633a24..2635aaca 100644 --- 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; |