On Sat, 13 Aug 2022, Sasha Levin wrote: > This is a note to let you know that I've just added the patch titled > > serial: Store character timing information to uart_port > > to the 5.18-stable tree which can be found at: > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > > The filename of the patch is: > serial-store-character-timing-information-to-uart_po.patch > and it can be found in the queue-5.18 subdirectory. > > If you, or anyone else, feels it should not be added to the stable tree, > please let <stable@xxxxxxxxxxxxxxx> know about it. > > commit 5517053a2e0b30a1e35f90504446af4a2c4920e8 > Author: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> > Date: Mon Apr 25 17:33:58 2022 +0300 > > serial: Store character timing information to uart_port > > [ Upstream commit 31f6bd7fad3b149a1eb6f67fc2e742e4df369b3d ] > > Struct uart_port currently stores FIFO timeout. Having character timing > information readily available is useful. Even serial core itself > determines char_time from port->timeout using inverse calculation. > > Store frame_time directly into uart_port. Character time is stored in > nanoseconds to have reasonable precision with high rates. To avoid > overflow, 64-bit math is necessary. > > It might be possible to determine timeout from frame_time by > multiplying it with fifosize as needed but only part of the users seem > to be protected by a lock. Thus, this patch does not pursue storing > only frame_time in uart_port. > > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/r/20220425143410.12703-2-ilpo.jarvinen@xxxxxxxxxxxxxxx > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> > > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > index 95d8d1fcd543..6b07b7b41354 100644 > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -24,6 +24,7 @@ > #include <linux/sysrq.h> > #include <linux/delay.h> > #include <linux/mutex.h> > +#include <linux/math64.h> > #include <linux/security.h> > > #include <linux/irq.h> > @@ -333,15 +334,18 @@ void > uart_update_timeout(struct uart_port *port, unsigned int cflag, > unsigned int baud) > { > - unsigned int size; > + unsigned int size = tty_get_frame_size(cflag); > + u64 frame_time; > > - size = tty_get_frame_size(cflag) * port->fifosize; > + frame_time = (u64)size * NSEC_PER_SEC; > + size *= port->fifosize; > > /* > * Figure the timeout to send the above number of bits. > * Add .02 seconds of slop > */ > port->timeout = (HZ * size) / baud + HZ/50; > + port->frame_time = DIV64_U64_ROUND_UP(frame_time, baud); > } > EXPORT_SYMBOL(uart_update_timeout); > > @@ -1610,10 +1614,8 @@ static void uart_wait_until_sent(struct tty_struct *tty, int timeout) > * Note: we have to use pretty tight timings here to satisfy > * the NIST-PCTS. > */ > - char_time = (port->timeout - HZ/50) / port->fifosize; > - char_time = char_time / 5; > - if (char_time == 0) > - char_time = 1; > + char_time = max(nsecs_to_jiffies(port->frame_time / 5), 1UL); > + > if (timeout && timeout < char_time) > char_time = timeout; > > diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h > index ca57d686d4d1..409573ea5ea4 100644 > --- a/include/linux/serial_core.h > +++ b/include/linux/serial_core.h > @@ -232,6 +232,7 @@ struct uart_port { > int hw_stopped; /* sw-assisted CTS flow state */ > unsigned int mctrl; /* current modem ctrl settings */ > unsigned int timeout; /* character-based timeout */ > + unsigned int frame_time; /* frame timing in ns */ > unsigned int type; /* port type */ > const struct uart_ops *ops; > unsigned int custom_divisor; > Why is this change necessary for stable? The change was made simply to make some other feature changes following a lot simpler but I don't think there is any known bug/issue it would be fixing. -- i.
