On Monday 28 July 2014 10:23:57 Graeme Gregory wrote: > The PL011 UART is the use-case I keep hitting, that IP block has a > variable input clock on pretty much everything I have seen in the wild. Ok, I see. What does ACPI-5.1 say about pl011? Interestingly, the subset of pl011 that is specified by SBSA does not contain the IBRD/FBRD registers, effectively making it a fixed-rated UART (I guess that would be a ART, without the U then), and you consequently don't even need to know the clock rate. However, my guess is that most hardware in the real world contains an actual pl011 and it does make a lot of sense to allow setting the baud rate on it, which then requires knowing the input clock. If there is any hardware that implements just the SBSA-mandated subset rather than the full pl011, we should probably implement both in the kernel: a dumb driver that can only send and receive, and the more complex one that can set the bit rates and flow-control but that requires a standardized ACPI table with the input clock rate. Whether the two would belong into one file or two separate driver modules is something I can't tell, it would be up to the serial maintainers to decide. > I really hope that this use does not spread beyond a few essential > devices like the UART. IMO all real hardware should be the other side of > a PCIe bridge. I would definitely agree with that. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
