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SubjectRe: [PATCH] Make the Startech UART detection 'more correct'.
On Mon, Sep 08, 2003 at 01:54:31PM -0700, Tom Rini wrote:
> Hello. The following patches (vs 2.4 and 2.6) make the Startech UART
> detection 'more correct' The problem is that on with the Motorola
> MPC82xx line (8245 for example) it has an internal DUART that it claims
> to be PC16550D compatible, and it has an additional EFR (Enhanced
> Feature Register) at offset 0x2, like on the Startech UARTS. However,
> it is not a Startech, and when it's detected as such, FIFOs don't work.
> The fix for this is that the Startech UARTs have a 32 byte FIFO [1] and
> the MPC82xx DUARTs have a 16-byte FIFO [2], to check that the FIFO size
> is correct for a Startech.

size_fifo() is claimed to be unreliable at detecting the FIFO size,
so I don't feel safe about using it here.

I'd suggest something like:

serial_outp(port, UART_LCR, UART_LCR_DLAB);
efr = serial_in(port, UART_EFR);
if ((efr & 0xfc) == 0) {
serial_out(port, UART_EFR, 0xac | (efr & 3));
/* if top 6 bits return zero, its motorola */
if (serial_in(port, UART_EFR) == (efr & 3)) {
/* motorola port */
} else {
/* ST16C650V1 port */
}
/* restore old value */
serial_outb(port, UART_EFR, efr);
}

If you can guarantee that the lower two bits will always be zero, you can
drop the frobbing to ignore/preseve the lower two bits.

--
Russell King (rmk@arm.linux.org.uk) http://www.arm.linux.org.uk/personal/
Linux kernel maintainer of:
2.6 ARM Linux - http://www.arm.linux.org.uk/
2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
2.6 Serial core
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