Re: [PATCH 0/9] serial: Add Tegra Combined UART driver

[Pekka Pessi <ppessi@nvidia.com>]

Hi Thierry,

What is the use case for the mailbox driver? What kind of entity will be 
there consuming sent messages and sending messages to kernel?

--Pekka

On 10/26/2018 02:16 PM, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
>
> Hi everyone,
>
> this is a reworked version of Mikko's earlier proposal[0]. I've reworked
> the TCU driver itself so that it relies less on global variables as well
> as added a Kconfig option to allow the console support to be selected. I
> also fixed a couple of issues that manifested themselves as I was moving
> towards the IRQ driven mode (TCU was passing a pointer to a local
> variable which was getting stored in the mailbox's ring buffer and the
> data pointed at was becoming stale by the time the mailbox got around to
> dequeue it).
>
> The biggest bulk of the changes is in the mailbox driver. This series
> addresses all of Jassi's comments from back at the time. One notable
> additional change is that shared mailboxes are now interrupt driven,
> which removes the need for polling mode.
>
> Unfortunately there is still an issue because the TCU uses the mailbox
> in atomic context for both TTY and console modes, so we get a sleeping-
> while-atomic BUG when using mbox_client->tx_block = true in order to
> rate-limit mbox_send_message(). In order to work around this, I added a
> mechanism to mbox_send_message() that will allow blocking from atomic
> context if the mailbox controller implements the new ->flush() callback.
> For Tegra HSP shared mailboxes this is done by spinning on the shared
> mailbox register until the receiver has marked the mailbox as empty. I
> have been running this locally for a couple of days now and it works
> perfectly.
>
> Furthermore this series incorporates Mikko's work in progress on
> splitting up the mailbox controllers and allowing multiple controllers
> to match on the same device tree node during mbox_request_channel().
>
> Last but not least there are no build-time dependencies between the
> mailbox and serial drivers, so I think the easiest way to merge this is
> if Jassi picks up patches 1-5, Greg takes patches 6 & 7 and I pick up
> patches 8-9 into the Tegra tree.
>
> Thanks,
> Thierry
>
> [0]: https://lore.kernel.org/patchwork/project/lkml/list/?series=357641
>
> Mikko Perttunen (5):
>    mailbox: Allow multiple controllers per device
>    dt-bindings: tegra186-hsp: Add shared interrupts
>    dt-bindings: serial: Add bindings for nvidia,tegra194-tcu
>    arm64: tegra: Add nodes for TCU on Tegra194
>    arm64: tegra: Mark TCU as primary serial port on Tegra194 P2888
>
> Thierry Reding (4):
>    mailbox: Support blocking transfers in atomic context
>    mailbox: tegra-hsp: Add support for shared mailboxes
>    mailbox: tegra-hsp: Add suspend/resume support
>    serial: Add Tegra Combined UART driver
>
>   .../bindings/mailbox/nvidia,tegra186-hsp.txt  |   3 +
>   .../bindings/serial/nvidia,tegra194-tcu.txt   |  35 ++
>   .../arm64/boot/dts/nvidia/tegra194-p2888.dtsi |   2 +-
>   arch/arm64/boot/dts/nvidia/tegra194.dtsi      |  38 +-
>   drivers/mailbox/mailbox.c                     |  11 +-
>   drivers/mailbox/tegra-hsp.c                   | 495 +++++++++++++++---
>   drivers/tty/serial/Kconfig                    |  22 +
>   drivers/tty/serial/Makefile                   |   1 +
>   drivers/tty/serial/tegra-tcu.c                | 299 +++++++++++
>   include/linux/mailbox_controller.h            |   4 +
>   include/uapi/linux/serial_core.h              |   3 +
>   11 files changed, 847 insertions(+), 66 deletions(-)
>   create mode 100644 Documentation/devicetree/bindings/serial/nvidia,tegra194-tcu.txt
>   create mode 100644 drivers/tty/serial/tegra-tcu.c
>