On 04.04.2024 13:54:22, Esben Haabendal wrote: > >> In fsl_lpuart.c and uartlite.c a warning message is printed if/when this > >> timeout occurs. I am fine with doing that here as well... You mean the read_poll_timeout() in fsl_lpuart.c in lpuart_global_reset()? This looks like a totally different codepath to me. https://elixir.bootlin.com/linux/v6.8/source/drivers/tty/serial/fsl_lpuart.c#L2793 In the write callback the fsl_lpuart.c does a readb(); cpu_relax(); while loop. https://elixir.bootlin.com/linux/v6.8/source/drivers/tty/serial/fsl_lpuart.c#L629 https://elixir.bootlin.com/linux/v6.8/source/drivers/tty/serial/fsl_lpuart.c#L636 The other driver is ma35d1_serial.c and uses a timeout of 10ms and ignored the return value :/ > >> On a related note. I am unsure if 10 ms is a good choice for timeout. I > >> picked it because it seems like a common value used in many/most > >> drivers. But at least some drivers use something like 1 s, which to me > >> sounds more sane given that we cannot do any meaningful error handling > >> on timeout. > > > > Not having any experience with console drivers, I think the time to > > empty the FIFO depends on the size of the TX FIFO and the speed of the > > UART. > > > > With some numbers (FIFO size and UART speed) pulled out of thin air (and > > neglecting start/stop/parity bits): > > > > 32 bytes * 8 bit/byte / 9600 bit/s = 26.7ms > > I assume that typical console usage will have messages much larger than > 32 bytes. But on the other hand, most use cases will be 115200 bit/s. I think it's about the length of the TX FIFO, not the full console message. And yes, while 115200 bps is typical, the corner cases should work too. > But in general, I would be more comofortable with a 1 second timeout. It > should be more than large enough to handle all realistic cases. But > will avoid spinning forever if uart for some reason does never clear the > TXD bit. makes sense regards, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung Nürnberg | Phone: +49-5121-206917-129 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 |
Attachment:
signature.asc
Description: PGP signature
