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Re: [PATCH 3/5] tty/8250_dw: Add support for OCTEON UARTS.

To: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 3/5] tty/8250_dw: Add support for OCTEON UARTS.
From: David Daney <ddaney@caviumnetworks.com>
Date: Wed, 19 Jun 2013 09:45:28 -0700
Cc: David Daney <ddaney.cavm@gmail.com>, <linux-mips@linux-mips.org>, <ralf@linux-mips.org>, Jamie Iles <jamie@jamieiles.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jslaby@suse.cz>, <linux-serial@vger.kernel.org>, <linux-kernel@vger.kernel.org>, David Daney <david.daney@cavium.com>
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On 06/19/2013 03:01 AM, Arnd Bergmann wrote:
On Tuesday 18 June 2013 12:12:53 David Daney wrote:
+static unsigned int dw8250_serial_inq(struct uart_port *p, int offset)
+{
+       offset <<= p->regshift;
+
+       return (u8)__raw_readq(p->membase + offset);
+}
+
+static void dw8250_serial_outq(struct uart_port *p, int offset, int value)
+{
+       struct dw8250_data *d = p->private_data;
+
+       if (offset == UART_LCR)
+               d->last_lcr = value;
+
+       offset <<= p->regshift;
+       __raw_writeq(value, p->membase + offset);
+       dw8250_serial_inq(p, UART_LCR);
+}

This breaks building on 32 bit architectures as I found on my daily ARM
builds: __raw_writeq cannot be defined on architectures that don't have
native 64 bit data access instructions.

I will rework the patch to avoid this problem.


It's also wrong to use the
__raw_* variant, which is not guaranteed to be atomic and is not
endian-safe.

We do runtime probing and only use this function on platforms where it is appropriate, so atomicity is not an issue. As for endianess, I used the __raw_ variant precisely because it is correct for both big and little endian kernels.

David Daney



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