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

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Date:   Tue, 3 Jul 2018 09:40:16 +0300
From:   Mikko Perttunen <cyndis@...si.fi>
To:     Thierry Reding <thierry.reding@...il.com>
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 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@...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?

Correct.

Mikko

> 
> Thierry
>