Re: [PATCH v3 6/8] serial: Add Tegra Combined UART driver

From: Mikko Perttunen
Date: Tue Jul 03 2018 - 02:40:34 EST

On 02.07.2018 16:47, Thierry Reding wrote:
On Mon, Jul 02, 2018 at 04:30:07PM +0300, Mikko Perttunen wrote:
On 02.07.2018 16:18, Thierry Reding wrote:
On Mon, Jul 02, 2018 at 02:40:31PM +0300, Mikko Perttunen wrote:
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@xxxxxxxxxx>

- 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.
- 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?