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

[Graeme Gregory]

On Tue, Jan 20, 2015 at 02:52:21PM +0000, Graeme Gregory wrote:
> On Tue, Jan 20, 2015 at 02:33:00PM +0000, Andre Przywara wrote:
> > 
> > 
> > On 20/01/15 14:26, Graeme Gregory wrote:
> > > 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.
> > 
> > Are you using arm,sbsa-uart in the DT, but a default PL011 in the model
> > config? In my model the default PL011 version has a 16 byte FIFO only,
> > specifying:
> > -C bp.pl011_uart0.revision="r1p5"
> > upgrades this to the SBSA specified 32 byte FIFO size.
> > With this setting I don't see any character loses.
> > 
> Yes with this setting all works with untimed_fifos=0
> 
> I was not aware of the differences in versions thanks.
> 
Now I know how to correctly configure model I have now tested on FVP and
Juno so feel free to add my Tested-by:

Graeme