[PATCH 00/10] drivers: PL011: add ARM SBSA Generic UART support

[Graeme Gregory]

On Tue, Jan 20, 2015 at 01:55:01PM +0000, Andre Przywara wrote:
> Hi Graeme,
> 
> On 20/01/15 13:08, Graeme Gregory wrote:
> > On Fri, Jan 16, 2015 at 05:22:56PM +0000, Andre Przywara wrote:
> >> The ARM Server Base System Architecture[1] document describes a
> >> generic UART which is a subset of the PL011 UART.
> >> It lacks DMA support, baud rate control and modem status line
> >> control, among other things.
> >> The idea is to move the UART initialization and setup into the
> >> firmware (which does this job today already) and let the kernel just
> >> use the UART for sending and receiving characters.
> >>
> >> This patchset integrates support for this UART subset into the
> >> existing PL011 driver - basically by refactoring some
> >> functions and providing a new uart_ops structure for it. It also has
> >> a separate probe function to be not dependent on AMBA/PrimeCell.
> >> It provides a device tree binding, but can easily be adapted to other
> >> device configuration systems.
> >> Beside the obvious effect of code sharing reusing most of the PL011
> >> code has the advantage of not introducing another serial device
> >> prefix, so it can go with ttyAMA, which seems to be pretty common.
> >>
> >> This series relies on Dave's recent PL011 fix[2], which gets rid of
> >> the loopback trick to get the UART going. There is a repo at [3]
> >> (branch sbsa-uart/v1), which has this patch already integrated.
> >>
> >> Patch 1/10 contains a bug fix which applies to the PL011 part also,
> >> it should be considered regardless of the rest of the series.
> >> Patch 2-7 refactor some PL011 functions by splitting them up into
> >> smaller pieces, so that most of the code can be reused later by the
> >> SBSA part.
> >> Patch 8 and 9 introduce two new properties for the vendor structure,
> >> this is for SBSA functionality which cannot be controlled by
> >> separate uart_ops members only.
> >> Patch 10 then finally drops in the SBSA specific code, by providing
> >> a new uart_ops, vendor struct and probe function for it. Also the new
> >> device tree binding is documented.
> >>
> >> For testing you should be able to take any hardware which has a PL011
> >> and change the DT to use a "arm,sbsa-uart" compatible string.
> >> Of course testing with a real SBSA Generic UART is welcomed!
> >>
> > I have tested this series on Juno where it seems to work and also on FVP
> > model where there are some issues.
> > 
> > On the FVP when we enter usespace a couple of 32 character strings are
> > printed then nothing else. 32 Characters is a suspicious number.
> 
> Can you try to add:
> -C bp.pl011_uart0.untimed_fifos=0
> to your model command line? (given that your model supports this option)
> 
> We discovered that lately, also not sure how the default for this
> setting is handled these days in the various model versions.
> 
> We are about to investigate this here atm.
> This issue seems to be introduced by Dave's FIFO patch.
> 

With this setting userspace functions better but loses characters
fairly regularly.

Graeme