On Mon, Jul 02, 2018 at 04:30:07PM +0300, Mikko Perttunen wrote:

On 02.07.2018 16:18, Thierry Reding wrote:

quoted

On Mon, Jul 02, 2018 at 02:40:31PM +0300, Mikko Perttunen wrote:

quoted

The Tegra Combined UART (TCU) is a mailbox-based mechanism that allows
multiplexing multiple "virtual UARTs" into a single hardware serial
port. The TCU is the primary serial port on Tegra194 devices.

Add a TCU driver utilizing the mailbox framework, as the used mailboxes
are part of Tegra HSP blocks that are already controlled by the Tegra
HSP mailbox driver.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
---

Notes:
     v2:
     - Removed (void) casts for unused variables.
     - Changed the uart_set_options() call to be on one line, even if its
       over 80 characters.
     - Added defines for magic numbers.
     - Style fixes.
     - Changed Kconfig entry to depend on the Tegra HSP driver instead of
       just the mailbox framework.
     v3:
     - Removed FLUSH bit, as it's unnecessary and slows down printing
     - Removed call to uart_set_options
     - Added mbox_free_channel calls to remove()

  drivers/tty/serial/Kconfig       |   9 ++
  drivers/tty/serial/Makefile      |   1 +
  drivers/tty/serial/tegra-tcu.c   | 291 +++++++++++++++++++++++++++++++++++++++
  include/uapi/linux/serial_core.h |   3 +
  4 files changed, 304 insertions(+)
  create mode 100644 drivers/tty/serial/tegra-tcu.c

The driver looks good to me. But for my own understanding, is there some
way we can make use of the multiplexing? That is, could we add a
mechanism to have the driver filter out only a specific stream? Could we
also specify which stream to send data back to? What happens by default?
Which stream is data sent to?

There is no multiplexing on the producer/device side (i.e. what this driver
does). The mailbox specified in device tree specifies the stream we send
stuff to. The mailboxes are per-CPU (we use the CCPLEX mailbox here), so it
cannot really be changed.

Oh, I see, so there is one stream per pair of mailboxes? That is, the
mailboxes we specify in the DT define which stream we receive from and
send to?

Thierry