| Message ID | 1506690534-27302-3-git-send-email-ulrich.hecht+renesas@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Geert Uytterhoeven |
| Headers | show |
Hi Uli, On Fri, Sep 29, 2017 at 3:08 PM, Ulrich Hecht <ulrich.hecht+renesas@gmail.com> wrote: > HSCIF has facilities that allow moving the RX sampling point by between > -8 and 7 sampling cycles (one sampling cycles equals 1/15 of a bit > by default) to improve the error margin in case of slightly mismatched > bit rates between sender and receiver. > > This patch allows changing the default (0, meaning center) using the > sysfs attribute "rx_sampling_point". > > Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com> Thanks for your patch! Have you noticed any improvements by fiddling with the sampling point? While this patch is useful as an investigation tool due to the sysfs interface, I don't think it should be applied as-is. I guess the goal is to select automatically the optimal sampling point, based on requested bit rate and available clock input rates, right? Or perhaps you want to keep the sysfs interface, to accommodate a sender that uses an off bit rate, unbeknownst to Linux (and unsupported by Linux, as software can request standard bit rates only) and thus needs user configuration? If that is the case, perhaps the sysfs interface should not be provided the raw sampling point offset, but the actual bit rate used by the other side, so the driver can calculate the offset? > --- a/drivers/tty/serial/sh-sci.c > +++ b/drivers/tty/serial/sh-sci.c > @@ -153,6 +153,7 @@ struct sci_port { > struct timer_list rx_fifo_timer; > int rx_fifo_timeout; > u16 hscif_tot; > + u16 hscif_srhp; s16, or even s8? > > bool has_rtscts; > bool autorts; > @@ -992,6 +993,42 @@ static int sci_handle_breaks(struct uart_port *port) > return copied; > } > > +static ssize_t rx_sampling_point_show(struct device *dev, > + struct device_attribute *attr, > + char *buf) > +{ > + struct uart_port *port = dev_get_drvdata(dev); > + struct sci_port *sci = to_sci_port(port); > + > + return sprintf(buf, "%d\n", sci->hscif_srhp); ... else it will not output negative numbers here. > +} > + > +static ssize_t rx_sampling_point_store(struct device *dev, > + struct device_attribute *attr, > + const char *buf, > + size_t count) > +{ > + struct uart_port *port = dev_get_drvdata(dev); > + struct sci_port *sci = to_sci_port(port); > + int ret; > + long r; s8 or just int? > + > + ret = kstrtol(buf, 0, &r); kstrtos8() or kstrtoint()? > + if (ret) > + return ret; > + > + if (r < -8 || r > 7) > + return -EINVAL; > + > + sci->hscif_srhp = r; > + > + return count; > +} > + > +static DEVICE_ATTR(rx_sampling_point, 0644, > + rx_sampling_point_show, > + rx_sampling_point_store); > + > static int scif_set_rtrg(struct uart_port *port, int rx_trig) > { > unsigned int bits; > @@ -2378,8 +2415,6 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, > serial_port_out(port, SCSCR, scr_val | s->hscif_tot); > serial_port_out(port, SCSMR, smr_val); > serial_port_out(port, SCBRR, brr); > - if (sci_getreg(port, HSSRR)->size) > - serial_port_out(port, HSSRR, srr | HSCIF_SRE); Why have you moved the setting of HSSRR? AFAIK all bit rate settings should be completed before the one bit delay below. > /* Wait one bit interval */ > udelay((1000000 + (baud - 1)) / baud); > @@ -2393,6 +2428,18 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, > serial_port_out(port, SCSMR, smr_val); > } > > + if (sci_getreg(port, HSSRR)->size) { > + u16 hssrr = srr | HSCIF_SRE; > + > + if (s->hscif_srhp) { > + u16 srhp = (s->hscif_srhp << HSCIF_SRHP_SHIFT) & > + HSCIF_SRHP_MASK; > + > + hssrr |= HSCIF_SRDE | srhp; > + } > + serial_port_out(port, HSSRR, hssrr); > + } > + > sci_init_pins(port, termios->c_cflag); > > port->status &= ~UPSTAT_AUTOCTS; Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
On Fri, Sep 29, 2017 at 03:08:54PM +0200, Ulrich Hecht wrote: > HSCIF has facilities that allow moving the RX sampling point by between > -8 and 7 sampling cycles (one sampling cycles equals 1/15 of a bit > by default) to improve the error margin in case of slightly mismatched > bit rates between sender and receiver. > > This patch allows changing the default (0, meaning center) using the > sysfs attribute "rx_sampling_point". > > Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com> > --- > drivers/tty/serial/sh-sci.c | 62 +++++++++++++++++++++++++++++++++++++++++++-- > drivers/tty/serial/sh-sci.h | 4 +++ > 2 files changed, 64 insertions(+), 2 deletions(-) Adding random sysfs files for random serial ports isn't good, especially if you do not document them in Documentation/ABI. I don't want to see this, but if you write sysfs files in the future, here's some review comments: > +static DEVICE_ATTR(rx_sampling_point, 0644, > + rx_sampling_point_show, > + rx_sampling_point_store); DEVICE_ATTR_RW() > + if (port->port.type == PORT_HSCIF) { > + sysfs_remove_file(&dev->dev.kobj, > + &dev_attr_rx_sampling_point.attr); No driver code should ever call sysfs functions, this should be either: device_create_file() or properly use an attribute group. thanks, greg k-h
On Fri, Sep 29, 2017 at 03:08:54PM +0200, Ulrich Hecht wrote: > HSCIF has facilities that allow moving the RX sampling point by between > -8 and 7 sampling cycles (one sampling cycles equals 1/15 of a bit > by default) to improve the error margin in case of slightly mismatched > bit rates between sender and receiver. > > This patch allows changing the default (0, meaning center) using the > sysfs attribute "rx_sampling_point". > > Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com> Wasn't there a conclusion in a chat meeting we had how to move this forward? How much effort would be implementing that?
diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index 41bf910..924a393 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -153,6 +153,7 @@ struct sci_port { struct timer_list rx_fifo_timer; int rx_fifo_timeout; u16 hscif_tot; + u16 hscif_srhp; bool has_rtscts; bool autorts; @@ -992,6 +993,42 @@ static int sci_handle_breaks(struct uart_port *port) return copied; } +static ssize_t rx_sampling_point_show(struct device *dev, + struct device_attribute *attr, + char *buf) +{ + struct uart_port *port = dev_get_drvdata(dev); + struct sci_port *sci = to_sci_port(port); + + return sprintf(buf, "%d\n", sci->hscif_srhp); +} + +static ssize_t rx_sampling_point_store(struct device *dev, + struct device_attribute *attr, + const char *buf, + size_t count) +{ + struct uart_port *port = dev_get_drvdata(dev); + struct sci_port *sci = to_sci_port(port); + int ret; + long r; + + ret = kstrtol(buf, 0, &r); + if (ret) + return ret; + + if (r < -8 || r > 7) + return -EINVAL; + + sci->hscif_srhp = r; + + return count; +} + +static DEVICE_ATTR(rx_sampling_point, 0644, + rx_sampling_point_show, + rx_sampling_point_store); + static int scif_set_rtrg(struct uart_port *port, int rx_trig) { unsigned int bits; @@ -2378,8 +2415,6 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, serial_port_out(port, SCSCR, scr_val | s->hscif_tot); serial_port_out(port, SCSMR, smr_val); serial_port_out(port, SCBRR, brr); - if (sci_getreg(port, HSSRR)->size) - serial_port_out(port, HSSRR, srr | HSCIF_SRE); /* Wait one bit interval */ udelay((1000000 + (baud - 1)) / baud); @@ -2393,6 +2428,18 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, serial_port_out(port, SCSMR, smr_val); } + if (sci_getreg(port, HSSRR)->size) { + u16 hssrr = srr | HSCIF_SRE; + + if (s->hscif_srhp) { + u16 srhp = (s->hscif_srhp << HSCIF_SRHP_SHIFT) & + HSCIF_SRHP_MASK; + + hssrr |= HSCIF_SRDE | srhp; + } + serial_port_out(port, HSSRR, hssrr); + } + sci_init_pins(port, termios->c_cflag); port->status &= ~UPSTAT_AUTOCTS; @@ -2793,6 +2840,7 @@ static int sci_init_single(struct platform_device *dev, sci_port->rx_fifo_timeout = 0; sci_port->hscif_tot = 0; + sci_port->hscif_shrp = 0; /* SCIFA on sh7723 and sh7724 need a custom sampling rate that doesn't * match the SoC datasheet, this should be investigated. Let platform @@ -3013,6 +3061,10 @@ static int sci_remove(struct platform_device *dev) sysfs_remove_file(&dev->dev.kobj, &dev_attr_rx_fifo_timeout.attr); } + if (port->port.type == PORT_HSCIF) { + sysfs_remove_file(&dev->dev.kobj, + &dev_attr_rx_sampling_point.attr); + } return 0; } @@ -3206,6 +3258,12 @@ static int sci_probe(struct platform_device *dev) return ret; } } + if (sp->port.type == PORT_HSCIF) { + ret = sysfs_create_file(&dev->dev.kobj, + &dev_attr_rx_sampling_point.attr); + if (ret) + return ret; + } #ifdef CONFIG_SH_STANDARD_BIOS sh_bios_gdb_detach(); diff --git a/drivers/tty/serial/sh-sci.h b/drivers/tty/serial/sh-sci.h index 2b708cc..80958b2 100644 --- a/drivers/tty/serial/sh-sci.h +++ b/drivers/tty/serial/sh-sci.h @@ -129,6 +129,10 @@ enum { /* HSSRR HSCIF */ #define HSCIF_SRE BIT(15) /* Sampling Rate Register Enable */ +#define HSCIF_SRDE BIT(14) /* Sampling Point Register Enable */ + +#define HSCIF_SRHP_SHIFT 8 +#define HSCIF_SRHP_MASK 0x0f00 /* SCPCR (Serial Port Control Register), SCIFA/SCIFB only */ #define SCPCR_RTSC BIT(4) /* Serial Port RTS# Pin / Output Pin */
HSCIF has facilities that allow moving the RX sampling point by between -8 and 7 sampling cycles (one sampling cycles equals 1/15 of a bit by default) to improve the error margin in case of slightly mismatched bit rates between sender and receiver. This patch allows changing the default (0, meaning center) using the sysfs attribute "rx_sampling_point". Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com> --- drivers/tty/serial/sh-sci.c | 62 +++++++++++++++++++++++++++++++++++++++++++-- drivers/tty/serial/sh-sci.h | 4 +++ 2 files changed, 64 insertions(+), 2 deletions(-)