Date: Tue, 20 Jan 2009 11:43:56 -0800 From: Oleksandr Tymoshenko <gonzo@bluezbox.com> To: freebsd-hackers@freebsd.org Subject: uart and big-endian targets Message-ID: <4976297C.7020405@bluezbox.com>
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Yesterday I ran into a "problem" with uart(4) on big-endian MIPS
board. uart code treats registers as bytes and reads/writes them using
bus_space_read_1/bus_space_write_1. To handle word-aligned registers we
have regshft in uart_bas structure. It works for little-endian flags
where lowest byte resides at uart_base + (regnum << regshft) address
but for big endian targets actual data resides at
uart_base + ((regnum + 1) << regshft) - 1.
One way to solve it is to increase uart_base when setting uart_bas,
but it's not obvious and requires knowledge of uart(4) internals.
I think better solution would be to take into account endianess
when defining uart_regofs. Or if other BE devices have data in
highest byte new field should be added to uart_bas (defaulted to 0)
Any thoughts?
--
gonzo
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