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SubjectRe: [PATCH 2.6] Altix - ioc3 serial support
On Fri, Dec 16, 2005 at 04:33:26PM -0600, Pat Gefre wrote:
> The following patch adds driver support for a 2 port PCI IOC3-based
> serial card on Altix boxes:
>
> ftp://oss.sgi.com/projects/sn2/sn2-update/044-ioc3-support

Here's some comments on ioc3_serial.c. Could you look at them and
either resolve them or discuss further. Thanks.

+#include <linux/serialP.h>

I don't think you need this include.

+ the_port->timeout = ((the_port->fifosize * HZ * bits) / (baud / 10));
+ the_port->timeout += HZ / 50; /* Add .02 seconds of slop */
Please use uart_update_timeout() instead.

+ info = the_port->info;
+ if (info->tty) {
+ set_bit(TTY_IO_ERROR, &info->tty->flags);
+ clear_bit(TTY_IO_ERROR, &info->tty->flags);
+ if ((info->flags & ASYNC_SPD_MASK) == ASYNC_SPD_HI)
+ info->tty->alt_speed = 57600;
+ if ((info->flags & ASYNC_SPD_MASK) == ASYNC_SPD_VHI)
+ info->tty->alt_speed = 115200;
+ if ((info->flags & ASYNC_SPD_MASK) == ASYNC_SPD_SHI)
+ info->tty->alt_speed = 230400;
+ if ((info->flags & ASYNC_SPD_MASK) == ASYNC_SPD_WARP)
+ info->tty->alt_speed = 460800;
+ }
None of this is required. info->tty->alt_speed is not used by the
serial layer - it knows how to deal with this itself. Secondly,
setting and clearing TTY_IO_ERROR is pointless. Note that the serial
layer takes care of TTY_IO_ERROR handling for you.

+ /* set the speed of the serial port */
+ ioc3_change_speed(the_port, info->tty->termios, (struct termios *)0);
serial_core will call this for you at the appropriate time. Note that
you decided above to check whether info->tty was NULL. If it was this
will oops. Better just get rid of it anyway - it's not necessary.

+ /* Notify upper layer of carrier drop */
+ if ((port->ip_notify & N_DDCD)
+ && port->ip_port) {
+ the_port->icount.dcd = 0;
+ wake_up_interruptible
+ (&the_port->info->
+ delta_msr_wait);
+ }
Use uart_handle_dcd_change(). Setting port->icount.dcd to zero in
this case is wrong. It also makes no attempt at informing the upper
layers that a hangup occurred. Note that uart_handle_dcd_change()
exists so that you don't have to think about these semantics. You
will need to keep the wake_up_interruptible though.

+ if ((port->ip_notify & N_DDCD)
+ && (shadow & SHADOW_DCD)
+ && (port->ip_port)) {
+ the_port = port->ip_port;
+ the_port->icount.dcd = 1;
+ wake_up_interruptible
+ (&the_port->info->delta_msr_wait);
Ditto. icount.dcd is not the state of DCD. It is a counter for the
number of times DCD changes state.

+ if ((port->ip_notify & N_DCTS) && (port->ip_port)) {
+ the_port = port->ip_port;
+ the_port->icount.cts =
+ (shadow & SHADOW_CTS) ? 1 : 0;
+ wake_up_interruptible
+ (&the_port->info->delta_msr_wait);
+ }
Ditto, except uart_handle_cts_change().

+ the_port->lock = SPIN_LOCK_UNLOCKED;
+ spin_lock_init(&the_port->lock);

Not necessary - uart_add_one_port() does this for you for non-console
ports, and for console ports, it is assumed that the console code has
already initialised the spinlock.

+ if (request_count > TTY_FLIPBUF_SIZE - tty->flip.count)
+ request_count = TTY_FLIPBUF_SIZE - tty->flip.count;
+
+ if (request_count > 0) {
+ read_count = do_read(the_port, ch, request_count);
+ if (read_count > 0) {
+ flip = 1;
+ memcpy(tty->flip.char_buf_ptr, ch, read_count);
+ memset(tty->flip.flag_buf_ptr, TTY_NORMAL, read_count);
+ tty->flip.char_buf_ptr += read_count;
+ tty->flip.flag_buf_ptr += read_count;
+ tty->flip.count += read_count;
+ the_port->icount.rx += read_count;
+ }
+ }
Please talk to Alan Cox about the best way to handle this. flip
buffers are going away.

+/**
+ * ic3_tx_empty - Is the transmitter empty? We pretend we're always empty
+ * @port: Port to operate on (we ignore since we always return 1)
+ *
+ */
+static unsigned int ic3_tx_empty(struct uart_port *the_port)
+{
+ return TIOCSER_TEMT;
+}
Not really a good idea if you care about the last bytes of data
in various buffers. Eg, cat file > /dev/yourport could well chop
off the last few characters for transmission.
Finally, you register the uart driver in ioc3uart_init(), and
unregister it in ioc3uart_remove() rather than ioc3uart_exit().
What if you have multiple boards? You remove one of them and
the uart driver gets unregistered? It doesn't look sane.

Haven't looked at the rest of the code tho.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
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