Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 

On 11-12-07 14:50, David Newall wrote:


Rene Herman wrote:
This particular discussion isn't about anything in general but solely about the delay an outb_p gives you on x86 since what is under discussion is not using an output to port 0x80 on that platform to generate it. 

That could be true if outb_p were used only in architecture dependent
It not only could be, it _is_ true. Not using an output to port 0x80 is what this discussion is about.
code, but it's not. It's used in drivers that are supposed to run on all sorts of platforms. Why does a megaraid controller need delays on i386 but not on Sparc, PowerPC, Alpha and others? Is it buggy on most platforms, or just unnecessarily slow on Intel?
The latter probably and I don't bleedin' well care. In a discussion about removing the out to 0x80 the only thing that is relevant is what it should be replaced with. Usually, "nothing" will do but generally, udelay(1) will. 


is needed, wouldn't you use a real delay; one that says how long it
should be?

Thinking that _p gives a pause is perhaps too PC-centric. Why, if a delay
Because any possible outb_p delay should be synced to the bus-clock, not to any wall-clock. 

You misunderstand.  A delay can be counted in bus cycles.
No damnit, you misunderstand. I'm saying that an outb_p _should_ be defined in terms of the bus clock since if you want a wall-clock delay you should be using just that.
The _hardware_ is synced to the bus clock and therefore, having a delay available that is synced to the bus clock as well makes some sense. And again again again again not withstanding that, a udelay will still be an okay replacement in practice. 

Rene.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/
[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux