On Wed, Mar 04, 2015 at 05:47:40PM +0000, Andre Przywara wrote: > Philip, > > sorry for the late reply, that was stuck in my Drafts folder :-( > > On 02/17/2015 04:16 PM, Dave P Martin wrote: > > On Tue, Feb 17, 2015 at 10:55:35AM -0500, Philip Elcan wrote: [...] > >> I'm a little late to address this patchset, but the SBSA defines all > >> the Generic UART registers 32-bit wide. However, the amba-pl011 driver > >> uses 16-bit accessors. How will you be handling that? Can the ARM PL011 > >> hardware handle 32-bit access? > > > > Interesting question. The PL011 TRM [1] specifies only a 16-bit-wide > > APB bus interface, but does not say that 32-bit accesses won't work. > > > > I suspect that 32-bit accesses will work on all or most PL011s -- if > > that looks too risky or we can't find enough test platforms to be sure > > of this, then we could maybe abstract the register access size as a > > quirk. > > > > Andre may already have an answer on this. > > I am not sure if the 32-bit register _width_ mentioned in the spec > really mandates 32-bit accesses, also the width may be just a spec bug. > Since the SBSA states that an ARM PL011r1p5 is a valid SBSA-UART > implementation, I wonder how this goes together. Also the highest > non-reserved bit in the registers is bit 15 in PL011 and bit 11 in the > SBSA subset. > > I fear the actual bus connection is an implementation detail. Given the > fact that all existing PL011 hardware so far works with the 16bit > accesses, I don't dare to change this. > > So I'd suggest to keep it as readw/writew for now and the revisit this > topic if some SBSA UART users complain. That makes it easier to justify > the rather invasive change to all MMIO accessors (which I already tried > on one machine for now without problems, btw). +1 As I understand it, the PL011 bus interface does not take access size into account at all, so providing "large-enough" accesses are used to cover all the bits meaningful to the UART, things are likely to work fine -- and this seems to be the case for all platforms currently supported by the amba-pl011 driver. Cheers ---Dave -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
