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

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Message-ID: <20180702131851.GH13096@ulmo>
Date:   Mon, 2 Jul 2018 15:18:51 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Mikko Perttunen <mperttunen@...dia.com>
Cc:     jassisinghbrar@...il.com, gregkh@...uxfoundation.org,
        jonathanh@...dia.com, devicetree@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/8] serial: Add Tegra Combined UART driver

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?

Thierry

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