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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>
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