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

Thierry Reding
2018-07-02T13:47:40Z

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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@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

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