linux-kernel - [PATCH v5] serial: sh-sci: Update the suspend/resume support

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Message-ID: <20250205093108.2027894-1-claudiu.beznea.uj@bp.renesas.com>
Date: Wed,  5 Feb 2025 11:31:08 +0200
From: Claudiu <claudiu.beznea@...on.dev>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	p.zabel@...gutronix.de,
	geert+renesas@...der.be,
	wsa+renesas@...g-engineering.com,
	prabhakar.mahadev-lad.rj@...renesas.com
Cc: claudiu.beznea@...on.dev,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: [PATCH v5] serial: sh-sci: Update the suspend/resume support

From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

The Renesas RZ/G3S supports a power saving mode where power to most of the
SoC components is turned off. When returning from this power saving mode,
SoC components need to be re-configured.

The SCIFs on the Renesas RZ/G3S need to be re-configured as well when
returning from this power saving mode. The sh-sci code already configures
the SCIF clocks, power domain and registers by calling uart_resume_port()
in sci_resume(). On suspend path the SCIF UART ports are suspended
accordingly (by calling uart_suspend_port() in sci_suspend()). The only
missing setting is the reset signal. For this assert/de-assert the reset
signal on driver suspend/resume.

In case the no_console_suspend is specified by the user, the registers need
to be saved on suspend path and restore on resume path. To do this the
sci_console_save_restore() function was added. There is no need to
cache/restore the status or FIFO registers. Only the control registers.
The registers that will be saved/restored on suspend/resume are
specified by the struct sci_suspend_regs data structure.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
---

The v4 of this patch was part of a series with 4 patches. As the rest of
the patches were applied I dropped the cover letter. The v4 cover letter
is located here:
https://lore.kernel.org/all/20250120130936.1080069-1-claudiu.beznea.uj@bp.renesas.com

Changes in v5:
- fixed typo in patch description
- adjusted the patch description to reflect the new patch content
- added struct sci_suspend_regs and dropped the suspend_cacheable
  flag introduced previously in struct plat_sci_reg; along with it
  the updates in sci_port_params[] were also dropped;
  also, the function (now sci_console_save_restore()) that saves
  and restores the registers content was adjusted accordingly
- s/sci_console_setup/sci_console_save_restore/g

Changes in v4:
- none

Changes in v3:
- none

Changes in v2:
- rebased on top of the update version of patch 2/8 from
  this series

 drivers/tty/serial/sh-sci.c | 55 +++++++++++++++++++++++++++++++++++--
 1 file changed, 53 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index b1ea48f38248..03349bc31080 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -104,6 +104,15 @@ struct plat_sci_reg {
 	u8 offset, size;
 };
 
+struct sci_suspend_regs {
+	u16 scsmr;
+	u16 scscr;
+	u16 scfcr;
+	u16 scsptr;
+	u8 scbrr;
+	u8 semr;
+};
+
 struct sci_port_params {
 	const struct plat_sci_reg regs[SCIx_NR_REGS];
 	unsigned int fifosize;
@@ -134,6 +143,8 @@ struct sci_port {
 	struct dma_chan			*chan_tx;
 	struct dma_chan			*chan_rx;
 
+	struct reset_control		*rstc;
+
 #ifdef CONFIG_SERIAL_SH_SCI_DMA
 	struct dma_chan			*chan_tx_saved;
 	struct dma_chan			*chan_rx_saved;
@@ -153,6 +164,7 @@ struct sci_port {
 	int				rx_trigger;
 	struct timer_list		rx_fifo_timer;
 	int				rx_fifo_timeout;
+	struct sci_suspend_regs		suspend_regs;
 	u16				hscif_tot;
 
 	bool has_rtscts;
@@ -3374,6 +3386,7 @@ static struct plat_sci_port *sci_parse_dt(struct platform_device *pdev,
 	}
 
 	sp = &sci_ports[id];
+	sp->rstc = rstc;
 	*dev_id = id;
 
 	p->type = SCI_OF_TYPE(data);
@@ -3546,13 +3559,41 @@ static int sci_probe(struct platform_device *dev)
 	return 0;
 }
 
+static void sci_console_save_restore(struct sci_port *s, bool save)
+{
+	struct sci_suspend_regs *regs = &s->suspend_regs;
+	struct uart_port *port = &s->port;
+
+	if (save) {
+		regs->scsmr = sci_serial_in(port, SCSMR);
+		regs->scscr = sci_serial_in(port, SCSCR);
+		regs->scfcr = sci_serial_in(port, SCFCR);
+		regs->scsptr = sci_serial_in(port, SCSPTR);
+		regs->scbrr = sci_serial_in(port, SCBRR);
+		regs->semr = sci_serial_in(port, SEMR);
+	} else {
+		sci_serial_out(port, SCSMR, regs->scsmr);
+		sci_serial_out(port, SCSCR, regs->scscr);
+		sci_serial_out(port, SCFCR, regs->scfcr);
+		sci_serial_out(port, SCSPTR, regs->scsptr);
+		sci_serial_out(port, SCBRR, regs->scbrr);
+		sci_serial_out(port, SEMR, regs->semr);
+	}
+}
+
 static __maybe_unused int sci_suspend(struct device *dev)
 {
 	struct sci_port *sport = dev_get_drvdata(dev);
 
-	if (sport)
+	if (sport) {
 		uart_suspend_port(&sci_uart_driver, &sport->port);
 
+		if (!console_suspend_enabled && uart_console(&sport->port))
+			sci_console_save_restore(sport, true);
+		else
+			return reset_control_assert(sport->rstc);
+	}
+
 	return 0;
 }
 
@@ -3560,8 +3601,18 @@ static __maybe_unused int sci_resume(struct device *dev)
 {
 	struct sci_port *sport = dev_get_drvdata(dev);
 
-	if (sport)
+	if (sport) {
+		if (!console_suspend_enabled && uart_console(&sport->port)) {
+			sci_console_save_restore(sport, false);
+		} else {
+			int ret = reset_control_deassert(sport->rstc);
+
+			if (ret)
+				return ret;
+		}
+
 		uart_resume_port(&sci_uart_driver, &sport->port);
+	}
 
 	return 0;
 }
-- 
2.43.0