* Re: [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation
2019-04-01 11:25 [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation Geert Uytterhoeven
@ 2019-04-01 12:12 ` Mukesh Ojha
2019-04-01 15:05 ` Ulrich Hecht
2019-04-04 9:45 ` Eugeniu Rosca
2 siblings, 0 replies; 4+ messages in thread
From: Mukesh Ojha @ 2019-04-01 12:12 UTC (permalink / raw)
To: Geert Uytterhoeven, Greg Kroah-Hartman, Jiri Slaby, Ulrich Hecht
Cc: Eugeniu Rosca, Dirk Behme, linux-serial, linux-kernel
On 4/1/2019 4:55 PM, Geert Uytterhoeven wrote:
> There are several issues with the formula used for calculating the
> deviation from the intended rate:
> 1. While min_err and last_stop are signed, srr and baud are unsigned.
> Hence the signed values are promoted to unsigned, which will lead
> to a bogus value of deviation if min_err is negative,
> 2. Srr is the register field value, which is one less than the actual
> sampling rate factor,
> 3. The divisions do not use rounding.
>
> Fix this by casting unsigned variables to int, adding one to srr, and
> using a single DIV_ROUND_CLOSEST().
>
> Fixes: 63ba1e00f178a448 ("serial: sh-sci: Support for HSCIF RX sampling point adjustment")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Cheers,
-Mukesh
> ---
> Anyone with a good test setup for verifying this feature actually works
> as advertised?
> ---
> drivers/tty/serial/sh-sci.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index 2bdaeba5d527a6ce..8dea59edde34c224 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -2522,7 +2522,9 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
> * center of the last stop bit in sampling clocks.
> */
> int last_stop = bits * 2 - 1;
> - int deviation = min_err * srr * last_stop / 2 / baud;
> + int deviation = DIV_ROUND_CLOSEST(min_err * last_stop *
> + (int)(srr + 1),
> + 2 * (int)baud);
>
> if (abs(deviation) >= 2) {
> /* At least two sampling clocks off at the
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation
2019-04-01 11:25 [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation Geert Uytterhoeven
2019-04-01 12:12 ` Mukesh Ojha
@ 2019-04-01 15:05 ` Ulrich Hecht
2019-04-04 9:45 ` Eugeniu Rosca
2 siblings, 0 replies; 4+ messages in thread
From: Ulrich Hecht @ 2019-04-01 15:05 UTC (permalink / raw)
To: Geert Uytterhoeven, Greg Kroah-Hartman, Jiri Slaby, Ulrich Hecht
Cc: Eugeniu Rosca, Dirk Behme, linux-serial, linux-kernel
> On April 1, 2019 at 1:25 PM Geert Uytterhoeven <geert+renesas@glider.be> wrote:
>
>
> There are several issues with the formula used for calculating the
> deviation from the intended rate:
> 1. While min_err and last_stop are signed, srr and baud are unsigned.
> Hence the signed values are promoted to unsigned, which will lead
> to a bogus value of deviation if min_err is negative,
> 2. Srr is the register field value, which is one less than the actual
> sampling rate factor,
> 3. The divisions do not use rounding.
>
> Fix this by casting unsigned variables to int, adding one to srr, and
> using a single DIV_ROUND_CLOSEST().
>
> Fixes: 63ba1e00f178a448 ("serial: sh-sci: Support for HSCIF RX sampling point adjustment")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
CU
Uli
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation
2019-04-01 11:25 [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation Geert Uytterhoeven
2019-04-01 12:12 ` Mukesh Ojha
2019-04-01 15:05 ` Ulrich Hecht
@ 2019-04-04 9:45 ` Eugeniu Rosca
2 siblings, 0 replies; 4+ messages in thread
From: Eugeniu Rosca @ 2019-04-04 9:45 UTC (permalink / raw)
To: Geert Uytterhoeven
Cc: Greg Kroah-Hartman, Jiri Slaby, Ulrich Hecht, Dirk Behme,
linux-serial, linux-kernel, Simon Herkenhoff, Eugeniu Rosca
Hi Geert,
On Mon, Apr 01, 2019 at 01:25:10PM +0200, Geert Uytterhoeven wrote:
> There are several issues with the formula used for calculating the
> deviation from the intended rate:
> 1. While min_err and last_stop are signed, srr and baud are unsigned.
> Hence the signed values are promoted to unsigned, which will lead
> to a bogus value of deviation if min_err is negative,
> 2. Srr is the register field value, which is one less than the actual
> sampling rate factor,
> 3. The divisions do not use rounding.
>
> Fix this by casting unsigned variables to int, adding one to srr, and
> using a single DIV_ROUND_CLOSEST().
>
> Fixes: 63ba1e00f178a448 ("serial: sh-sci: Support for HSCIF RX sampling point adjustment")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> Anyone with a good test setup for verifying this feature actually works
> as advertised?
> ---
> drivers/tty/serial/sh-sci.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index 2bdaeba5d527a6ce..8dea59edde34c224 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -2522,7 +2522,9 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
> * center of the last stop bit in sampling clocks.
> */
> int last_stop = bits * 2 - 1;
> - int deviation = min_err * srr * last_stop / 2 / baud;
> + int deviation = DIV_ROUND_CLOSEST(min_err * last_stop *
> + (int)(srr + 1),
> + 2 * (int)baud);
>
> if (abs(deviation) >= 2) {
> /* At least two sampling clocks off at the
Just wanted to say thank you for your tremendous commitment and
continuity in supporting the R-Car platform (and beyond that), which
allowed us to gracefully overcome the problems encountered in the
project in the best possible time, specifically thanks to this patch.
Best regards,
Eugeniu.
^ permalink raw reply [flat|nested] 4+ messages in thread