On 11/23/2016 02:01 AM, Sascha Hauer wrote:

With this patch the serial core provides LED triggers for RX and TX.

As the serial core layer does not know when the hardware actually sends
or receives characters, this needs help from the UART drivers.

Looking at 8250, we call serial8250_tx_chars from __start_tx which is
called form the uart_ops::start_tx, for RX I sort of agree, since this
happens in interrupt handler. I suppose some drivers could actually
queue work but not do it right away though?

The LED triggers are registered in uart_add_led_triggers() called from
the UART drivers which want to support LED triggers. All the driver
has to do then is to call uart_led_trigger_[tx|rx] to indicate
activity.

Could we somehow remedy the lack of knowledge from the core as whether
the HW sends/receives characters first before adding support for LED
triggers? It would be more generic and future proof to require UART
drivers to report to the core when they actually TX/RX, and then at the
core level, utilize that knowledge to perform the LED trigger.

Side note: are you positive using drv->dev_name is robust enough on
systems with many different UART drivers, yet all of them being ttyS*?

Thanks!
-- 
Florian