From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King Subject: Re: [PATCH] Make the Startech UART detection 'more correct'. Date: Tue, 9 Sep 2003 17:18:59 +0100 Sender: linux-kernel-owner@vger.kernel.org Message-ID: <20030909171859.D4216@flint.arm.linux.org.uk> References: <20030908205431.GB3888@ip68-0-152-218.tc.ph.cox.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20030908205431.GB3888@ip68-0-152-218.tc.ph.cox.net>; from trini@kernel.crashing.org on Mon, Sep 08, 2003 at 01:54:31PM -0700 To: Tom Rini Cc: tytso@mit.edu, Kernel Mailing List , linux-serial@vger.kernel.org, gallen@arlut.utexas.edu List-Id: linux-serial@vger.kernel.org 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