* Re: Patch "serial: Store character timing information to uart_port" has been added to the 5.18-stable tree
[not found] <20220813215542.1973126-1-sashal@kernel.org>
@ 2022-08-15 10:54 ` Ilpo Järvinen
2022-08-15 12:44 ` Greg Kroah-Hartman
0 siblings, 1 reply; 2+ messages in thread
From: Ilpo Järvinen @ 2022-08-15 10:54 UTC (permalink / raw)
To: Sasha Levin; +Cc: stable-commits, Greg Kroah-Hartman, Jiri Slaby, stable
[-- Attachment #1: Type: text/plain, Size: 4129 bytes --]
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@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.com
> 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.
--
i.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Patch "serial: Store character timing information to uart_port" has been added to the 5.18-stable tree
2022-08-15 10:54 ` Patch "serial: Store character timing information to uart_port" has been added to the 5.18-stable tree Ilpo Järvinen
@ 2022-08-15 12:44 ` Greg Kroah-Hartman
0 siblings, 0 replies; 2+ messages in thread
From: Greg Kroah-Hartman @ 2022-08-15 12:44 UTC (permalink / raw)
To: Ilpo Järvinen; +Cc: Sasha Levin, stable-commits, Jiri Slaby, stable
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;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@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.com
> > 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
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2022-08-15 10:54 ` Patch "serial: Store character timing information to uart_port" has been added to the 5.18-stable tree Ilpo Järvinen
2022-08-15 12:44 ` Greg Kroah-Hartman
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