--- Arjan van de Ven <arjan@xxxxxxxxxxxxx> wrote: > On Thu, 2005-03-31 at 12:18 -0800, john bogus wrote: > > I have seen various examples in the kernel code > where > > a bit is set / cleared in an output port by code > like > > > > writeb((readb(PBDDR)) & PORTB_PIN0_SDA_INPUT, > PBDDR); > > > > or > > > > uiRegTemp = inl(GPIO_PADDR); > > outl( uiRegTemp | 0x80, GPIO_PADDR ); > > > > > > This code is not atomic (and in some examples I am > > guessing it should be). Are there fuctions > similar to > > set_bit, clear_bit, change_bit which work on I/O? > if > > not what is the recomended way to do this? > > this is not how pci busses and such work. > THe pci bus only has read and write primitives on 8 > 16 and 32 bit sizes. > No bit level ops. > This is often used in embedded applications, in my case I am using an EP9301 processor. As you indicated it does not have bit operations. It is often the case that different drivers will use bits on the same port. To get bit ops you read the port change the bit and write the result back. The problem with this is that if the operation is interrupted between the read and the write and the port is changed by another process, the change by the other process will be lost when it returns control to this process, thus the need for atomic operations. Normally I would just disable/enable interrupts around the read/write, but this seems to be strongly discouraged in linux. __________________________________ Do you Yahoo!? Yahoo! Personals - Better first dates. More second dates. http://personals.yahoo.com -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
