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Date: Mon, 28 Jul 2014 12:46:17 +0200 From: Arnd Bergmann <arnd@...db.de> To: Graeme Gregory <graeme.gregory@...aro.org> Cc: linux-arm-kernel@...ts.infradead.org, Olof Johansson <olof@...om.net>, Hanjun Guo <hanjun.guo@...aro.org>, Mark Rutland <mark.rutland@....com>, Mark Brown <broonie@...aro.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Lv Zheng <lv.zheng@...el.com>, Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>, Daniel Lezcano <daniel.lezcano@...aro.org>, Robert Moore <robert.moore@...el.com>, "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>, Grant Likely <grant.likely@...aro.org>, Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>, Robert Richter <rric@...nel.org>, Jason Cooper <jason@...edaemon.net>, Marc Zyngier <marc.zyngier@....com>, Liviu Dudau <Liviu.Dudau@....com>, Bjorn Helgaas <bhelgaas@...gle.com>, Randy Dunlap <rdunlap@...radead.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Sudeep Holla <Sudeep.Holla@....com> Subject: Re: [PATCH 19/19] Documentation: ACPI for ARM64 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-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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