On Mon, Aug 15, 2022 at 01:54:32PM +0300, Ilpo Järvinen wrote:

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%3Ba=su...

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@vger.kernel.org know about it.

commit 5517053a2e0b30a1e35f90504446af4a2c4920e8 Author: Ilpo Järvinen ilpo.jarvinen@linux.intel.com 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@linux.intel.com Link: https://lore.kernel.org/r/20220425143410.12703-2-ilpo.jarvinen@linux.intel.c... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org

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.

Good point, now dropped from 5.15.y and 5.18.y, thanks.

greg k-h