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

[Mikko Perttunen]

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>
> > > > ---
> > > >
> > > > 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?

Correct.

Mikko

> Thierry