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

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Date:   Mon, 2 Jul 2018 15:47:31 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Mikko Perttunen <cyndis@...si.fi>
Cc:     Mikko Perttunen <mperttunen@...dia.com>,
        devicetree@...r.kernel.org, gregkh@...uxfoundation.org,
        jassisinghbrar@...il.com, linux-kernel@...r.kernel.org,
        jonathanh@...dia.com, linux-serial@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 6/8] serial: Add Tegra Combined UART driver

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@...dia.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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