Re: [edk2-platforms][PATCH 0/4] Platform/RPi: Automate runtime UART selection

["Ard Biesheuvel" <ard.biesheuvel@linaro.org>]

On Tue, 28 Jan 2020 at 18:20, Pete Batard <pete@akeo.ie> wrote:
>
> The Raspberry Pi platform contains two UARTs, one PL011-based and the
> other (called miniUART) 16650-compatible, that are pinmuxed to the GPIO
> serial port according to whether a Device Tree overlay is present in
> config.txt or not. In most cases, it takes only the user commenting
> or uncommenting an overlay line in their config to switch between PL011
> and miniUART.
>
> As such, the use of a build time option to select the UART should be
> avoided when it is effectively possible to detect which of the UART
> is in use at runtime, through an MMIO call.
>
> This series of patches achieves just this by:
>
> * Adding the relevant clock manager constant to Silicon (which we'll
>   need to retrieve the VPU divisor, needed to set the 16550 baudrate).
>
> * Adding a new DualSerialPortLibrary that handles runtime detection
>   and switching between PL011 and 16650.
>
> * Enabling the use of DualSerialPortLibrar for both the RPi3 and RPi4.
>
> Important notes:
>
> * This patch does not cover ACPI serial bindings, as this requires
>   switching to using DynamicTablesPkg / ConfigurationManagerDxe to
>   generate the ACPI tables at runtime. As such, each of the RPi
>   platforms is currently hardcoded to use one of the UARTs for ACPI:
>   miniUART for RPi3 and PL011 for RPi4. Of course, there is no issue
>   for Device Tree usage, since the relevant UART overlay will have
>   been applied then. We don't see the current ACPI UART hardcoding
>   as a major issue, as this doesn't change anything for RPi3 and we
>   expect RPi4 users to prefer PL011 over miniUART anyway, but we
>   will look into using DynamicTablesPkg once we see clearer in terms
>   of ACPI for RPi4.
>
> * There is work underway to produce a PL011 vs miniUART aware TF-A,
>   which we hope will be completed by the next TF-A release. Once
>   that release has occurred, we will update the TF-A blobs in
>   non-osi, since the ones we have right now are hardcoded to output
>   through one UART only.
>
> * One the subject of TF-A usage, there appears to be an issue when
>   using a 16650 (miniUART) based TF-A in a PL011 configuration as
>   the system freezes then. This issue does not occur when using a
>   PL011 based TF-A in a 16650/miniUART configuration (which is one
>   of the the reason why we picked the PL011 TF-A binary over the
>   16650 one for RPi4). What this means is that, unless you replace
>   the current RPi3 TF-A blobs from non-osi with a version that
>   outputs to PL011, and attempt to use a Raspberry Pi 3 in PL011
>   mode, then a boot freezout will happen before the UEFI firmware
>   gets a chance to apply UART runtime selection. This is an issue
>   that will of course resolve itself once we replace the current
>   TF-A  blobs with the upcoming runtime selection version. However,
>   I can also produce a patch that replaces the current 16650-based
>   RPI3 TF-A in non-osi with PL011-based ones, if we think it's
>   needed before we get the upcoming runtime selection TF-A binaries.
>
> * It appears that we are issuing serial write calls before the
>   UARTs are initialized, which is a problem if 16650 is being used
>   instead of PL011 (produces a freezout similar to what occurs when
>   using 16650 TF-A in a PL011 enabled conf). As such, we do perform
>   miniUART vs PL011 detection in both initialize and write.
>
> * The 16650 code applies the recent bugfix from Ashish Singhal in
>   https://edk2.groups.io/g/devel/message/53487.
>
> Regards,
>
> /Pete
>
> Pete Batard (4):
>   Silicon/Broadcom/Bcm283x: Add clock manager constants
>   Platform/RPi: Add serial lib for runtime PL011 vs miniUART detection
>   Platform/RPi3: Enable the use of DualSerialPortLib
>   Platform/RPi4: Enable the use of DualSerialPortLib
>

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Pushed as 9369b01e86ad..41c1d9ba3304

Thanks!

>  Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c   | 836 ++++++++++++++++++++
>  Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.inf |  55 ++
>  Platform/RaspberryPi/RPi3/RPi3.dsc                                   |  15 +-
>  Platform/RaspberryPi/RPi3/Readme.md                                  |   7 +
>  Platform/RaspberryPi/RPi4/AcpiTables/AcpiTables.inf                  |   7 +
>  Platform/RaspberryPi/RPi4/RPi4.dsc                                   |  26 +-
>  Platform/RaspberryPi/RPi4/RPi4.fdf                                   |   4 -
>  Platform/RaspberryPi/RPi4/Readme.md                                  |  21 +-
>  Silicon/Broadcom/Bcm283x/Include/IndustryStandard/Bcm2836.h          |  22 +
>  9 files changed, 944 insertions(+), 49 deletions(-)
>  create mode 100644 Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.c
>  create mode 100644 Platform/RaspberryPi/Library/DualSerialPortLib/DualSerialPortLib.inf
>
> --
> 2.21.0.windows.1
>