Re: Help on boot manager 'Boot Manager Menu' and direct boot

[Udit Kumar <udit.kumar@nxp.com>]

Hi Ard 

> -----Original Message-----
> From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Sent: Monday, December 3, 2018 7:35 PM
> To: Laszlo Ersek <lersek@redhat.com>
> Cc: Udit Kumar <udit.kumar@nxp.com>; Andrew Fish <afish@apple.com>; Leif
> Lindholm <leif.lindholm@linaro.org>; Ruiyu Ni <ruiyu.ni@intel.com>; edk2-
> devel@lists.01.org; Zeng, Star <star.zeng@intel.com>
> Subject: Re: [edk2] Help on boot manager 'Boot Manager Menu' and direct boot
> 
> On Mon, 3 Dec 2018 at 14:45, Laszlo Ersek <lersek@redhat.com> wrote:
> >
> > On 12/03/18 11:03, Udit Kumar wrote:
> > > Hi Laszlo
> > >
> > >> Are you using the latest edk2?
> > > Yes, when I hit the bug, first step was to move to latest edk2. But this didn't
> helped.
> > >
> > > I am not sure, why we are keeping PL011 Fifo mode off in default
> configuration.
> >
> > Sorry, I don't know: although the subject logic has gone through
> > several updates over time, the default that you point out seems to go
> > back to commit 051e63bb551a ("ArmPlatformPkg/PL011Uart: Allowed to
> > change UART settings in its initialization function", 2012-02-29). And
> > that commit doesn't explain the default.
> >
> 
> The default setting for
> gEfiMdePkgTokenSpaceGuid.PcdUartDefaultReceiveFifoDepth is 1 not 0, and so
> you will end up with a 1 character FIFO setting. I wonder if we could improve

Setting this Pcd to zero will fix problem for me, 
With  PcdUartDefaultReceiveFifoDepth as 1, we are disabling the Fifo at IP level whereas for 0 we are enabling IP fifo.

> PL011UartInitializePort () in PL011UartLib to deal with this better.

Suggest, if IP level Fifo can be kept enabled, always ?

> Note that this also affects platforms that can switch between DT and ACPI boot:
> the same PL011 is described as a 'dumb' SBSA uart in the latter case, and so it is
> up to the firmware to configure the UART FIFO correctly, or you will not be able
> to use the UART under the ACPI OS.

For my ACPI boot (without SPCR table), I hit the same issue.

OS  (Linux, not sure of other OSes) except FIFO to be enabled by firmware/boot-loader. 

Regards
Udit