On Sun, Jan 22, 2006 at 12:33:07AM -0800, Andrew Morton wrote:
> Russell King <[email protected]> wrote:
> >
> > On Sat, Jan 21, 2006 at 11:36:49PM -0800, Andrew Morton wrote:
> > > Atsushi Nemoto <[email protected]> wrote:
> > > >
> > > > serial_txx9_verify_port(struct uart_port *port, struct serial_struct *ser)
> > > > {
> > > > - if (ser->irq < 0 ||
> > > > - ser->baud_base < 9600 || ser->type != PORT_TXX9)
> > > > + unsigned long new_port = (unsigned long)ser->port +
> > > > + ((unsigned long)ser->port_high << ((sizeof(long) - sizeof(int)) * 8));
> > >
> > > Are you sure about this part? Shifting something left by sizeof(something)
> > > seems very strange. It'll give different results on 64-bit machines for
> > > the same hardware. Are you sure it wasn't supposed to be an addition?
> >
> > There is a definition for that constant - it's called HIGH_BITS_OFFSET.
>
> There are two definitions, actually. drivers/serial/serial_core.c and
> drivers/serial/8250.h.
>
> > No need to try to buggily recreate it.
>
> Where's the bug in the proposed code?
There isn't, but because it's wider than 80 columns, it got mis-read.
As demonstrated, the 80 column rule _still_ matters for readability.
> Can you tell us what HIGH_BITS_OFFSET actually does? Stuffing the port
> address into the upper 32-bits of a ulong on 64-bit machines. Am consumed
> by curiosity.
It's history. port in serial_struct has been declared as:
unsigned int port;
since the year dot, and has been exposed to userland since it's
inception. I guess that 64-bit machines came along, and this was
found to be inadequate. Rather than deprecate the current interface
and provide a sane API, whoever did this came up with this yucky
solution where
unsigned int port_high;
contains the address bits outside the range of "port". Presumably
they assumed that sizeof(unsigned long) == 2 * sizeof(unsigned int)
here. If not, this silly interface again breaks on us.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
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