On 18/05/2022 09:48, Greg KH wrote:> On Tue, May 17, 2022 at 07:42:46PM
+0100, linuxkernel wrote:
>> hello I, looking at writing a kernel driver for the Texas instruments
>> TPS92662A/TPS92663A which uses a "UART bus" e.g
>> |-----------| |-----------| |-----------| |-----------|
>> | | | TPS92662A | | TPS92662A | | TPS92663A |
>> | UART | | -Q1 | | -Q1 | | -Q1 |
>> | | | | | | | |
>> |-----------| |-----------| |-----------| |-----------|
>> | | | |
>> | | | |
>> | | | |
>> -----------------------------------------------------
>> and control communications by specific sequencing. configuring this
>> appears to require being able to pull RX Low
>>> The MCU unit can reset the device UART and protocol state machine at
>>> any time by holding the RX input low for a period of at least 12 bit
>>> times (16 × 12 CLK periods).
>> practically i can always pull RX low via other means, but if the UART
>> can do this it would be better and be more generic.
> How can your UART do that in a generic way? thanks, greg k-h sorry
im not sure i explained that clearly
i also appear to have, not got the previous diagram right, (corrected in
this reply for clarity) Im still getting used to plain text emails.
im not that familiar with UARTs in practice, and after re-reading i
think i could have phrased that better, as had issue with MCU/IC UART
TX/RX perspectives
e.g
|-----------| |-----------|
| TX|-----------|RX |
| MCU UART | | IC |
| RX|-----------|TX |
|-----------| |-----------|
from the mcu perspective its the TX pin, while from the RX pin from the
ICs perspective.
from that perspective i need to pull the ICs RX pin low which means pull
the MCU UART TX pin Low.
now this seems conceptually similar to a "break condition"
which some tty functions can produce
e.g
static int send_break(struct tty_struct *tty, unsigned int duration)
[https://elixir.bootlin.com/linux/latest/source/drivers tty/tty_io.c#L2461]
with which i might me half way to answering my own question
i can't see call to that via serdev, or equivalent
however the serdev code sits on top of the tty code
(http://events17.linuxfoundation.org/sites/events/files/slides/serdev-elce-2017-2.pdf#Outline0.11)
it appears i would have to somehow get to the underlying send_break()
function without breaking anything
which needs a vaild tty_struct which appears to be part of tty_port and
can get via
struct tty_struct *tty_port_tty_get(struct tty_port *port);
and it appears that you can get that via
struct serport *serport = serdev_controller_get_drvdata(ctrl);
and can get struct serdev_controller *ctrl from struct serdev_device
but doing that cleanly is another thing.
i could either try and write something like that into the driver or
could try and write a patch for serdev that effectively calls that
function in tty so a serdev device can request a break from itself
unless there is a alternative im not seeing.
if there is any advice you can give that would be helpful
kind regards
christopher tyerman
