[PATCH v15 6/7] spi: pxa2xx: restore LPSS private register state on S3 resume

Intel LPSS SPI controllers lose all private register state across S3
suspend because the LPSS power domain is fully removed. On resume the
driver only re-enables the SSP clock, leaving the LPSS private registers
in their power-on-reset state, which causes two problems:

1. LPSS_PRIV_RESETS (offset 0x04 within the LPSS private space) stays
   zero, keeping the functional block in reset. Any MMIO access while
   the block is held in reset causes a PCIe Completion Timeout and a
   watchdog-triggered system reset. LPSS_PRIV_RESETS_FUNC and
   LPSS_PRIV_RESETS_IDMA must be de-asserted before any other register
   access on resume.

2. The LPSS software chip-select control register must not be blindly
   restored from its suspend-time snapshot: if CS was asserted at the
   moment of suspend, restoring that state corrupts the first
   post-resume SPI transaction. Instead, call lpss_ssp_setup() which
   unconditionally writes SW_MODE | CS_HIGH (idle/deasserted), matching
   the state established at probe time.

To resolve these issues safely:
- Wrap S3 suspend/resume with pm_runtime_resume_and_get() and
  pm_runtime_put_autosuspend() to guarantee active clocks during MMIO
  access and preserve PM reference counting.
- Restrict LPSS private register save/restore to LPT, BYT, and BSW
  platforms via pxa2xx_spi_need_lpss_restore() (newer platforms are
  handled by intel-lpss.c).
- Save only the first 6 LPSS private registers (offsets 0x00..0x14) in
  drv_data during suspend, avoiding reserved offsets beyond 0x14.
- On resume, de-assert resets first, restore saved registers, call
  lpss_ssp_setup(), and clear drv_data->suspended to prevent unclocked
  IRQ access.
- Add error recovery paths for spi_controller_suspend/resume failures.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=108331
Signed-off-by: Shih-Yuan Lee <[email protected]>
---
 drivers/spi/spi-pxa2xx.c | 95 ++++++++++++++++++++++++++++++++++++++--
 drivers/spi/spi-pxa2xx.h |  1 +
 2 files changed, 92 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
index 88ed28096b07..56e434f6e794 100644
--- a/drivers/spi/spi-pxa2xx.c
+++ b/drivers/spi/spi-pxa2xx.c
@@ -72,6 +72,11 @@ struct chip_data {
 #define LPSS_CAPS_CS_EN_SHIFT			9
 #define LPSS_CAPS_CS_EN_MASK			(0xf << LPSS_CAPS_CS_EN_SHIFT)
 
+/* Offsets from drv_data->lpss_base */
+#define LPSS_PRIV_RESETS			0x04
+#define LPSS_PRIV_RESETS_IDMA			BIT(2)
+#define LPSS_PRIV_RESETS_FUNC			0x3
+
 #define LPSS_PRIV_CLOCK_GATE 0x38
 #define LPSS_PRIV_CLOCK_GATE_CLK_CTL_MASK	0x3
 #define LPSS_PRIV_CLOCK_GATE_CLK_CTL_FORCE_ON	0x3
@@ -189,6 +194,18 @@ static bool is_lpss_ssp(const struct driver_data *drv_data)
 	}
 }
 
+static bool pxa2xx_spi_need_lpss_restore(const struct driver_data *drv_data)
+{
+	switch (drv_data->ssp_type) {
+	case LPSS_LPT_SSP:
+	case LPSS_BYT_SSP:
+	case LPSS_BSW_SSP:
+		return true;
+	default:
+		return false;
+	}
+}
+
 static bool is_quark_x1000_ssp(const struct driver_data *drv_data)
 {
 	return drv_data->ssp_type == QUARK_X1000_SSP;
@@ -1527,17 +1544,45 @@ static int pxa2xx_spi_suspend(struct device *dev)
 	struct ssp_device *ssp = drv_data->ssp;
 	int status;
 
+	status = pm_runtime_resume_and_get(dev);
+	if (status < 0)
+		return status;
+
 	status = spi_controller_suspend(drv_data->controller);
 	if (status)
-		return status;
+		goto out_put;
 
+	/* Disable SSP interrupt generation on hardware level while clock is active */
 	pxa2xx_spi_off(drv_data);
+
+	/* Mark as suspended and synchronize IRQ before disabling clock */
 	drv_data->suspended = true;
 	synchronize_irq(ssp->irq);
 
+	if (pxa2xx_spi_need_lpss_restore(drv_data)) {
+		unsigned int i;
+
+		/*
+		 * Save the first 6 LPSS private registers (offsets 0x00 to 0x14)
+		 * while the clock is still enabled.  They are lost when the LPSS
+		 * power domain is removed across S3 and must be restored on resume.
+		 * Use drv_data->lpss_base so the correct per-platform offset
+		 * is applied regardless of LPSS IP revision.
+		 * Registers beyond 0x14 (except CS control at 0x18) are reserved
+		 * or unimplemented on LPT, and accessing them triggers a PCIe
+		 * Completion Timeout causing a system halt.
+		 */
+		for (i = 0; i < 6; i++)
+			drv_data->lpss_priv_ctx[i] = readl(drv_data->lpss_base + i * 4);
+	}
+
 	pxa2xx_spi_clk_disable(drv_data);
 
 	return 0;
+
+out_put:
+	pm_runtime_put_noidle(dev);
+	return status;
 }
 
 static int pxa2xx_spi_resume(struct device *dev)
@@ -1550,9 +1595,47 @@ static int pxa2xx_spi_resume(struct device *dev)
 	if (!pm_runtime_suspended(dev)) {
 		status = pxa2xx_spi_clk_enable(drv_data);
 		if (status)
-			return status;
+			goto out_put;
 	}
 
+	if (pxa2xx_spi_need_lpss_restore(drv_data)) {
+		unsigned int i;
+
+		/*
+		 * The LPSS power domain is removed across S3, taking
+		 * all private registers with it.  De-assert the
+		 * functional block and IDMA resets first; any MMIO
+		 * access while the block is held in reset causes a
+		 * PCIe Completion Timeout and a watchdog-triggered
+		 * system reset.
+		 */
+		writel(LPSS_PRIV_RESETS_FUNC | LPSS_PRIV_RESETS_IDMA,
+		       drv_data->lpss_base + LPSS_PRIV_RESETS);
+
+		/* Restore the other 5 saved private registers */
+		for (i = 0; i < 6; i++) {
+			if (i == LPSS_PRIV_RESETS / 4)
+				continue;
+			writel(drv_data->lpss_priv_ctx[i],
+			       drv_data->lpss_base + i * 4);
+		}
+	}
+
+	if (is_lpss_ssp(drv_data)) {
+		/*
+		 * Re-initialise the SW chip-select control register so
+		 * CS starts deasserted (SW_MODE | CS_HIGH), regardless
+		 * of the state it was in at suspend time.  A stale
+		 * asserted CS on the first post-resume transaction
+		 * corrupts the write-status response from the device.
+		 */
+		lpss_ssp_setup(drv_data);
+	}
+
+	/*
+	 * Now that resets are de-asserted and registers are restored,
+	 * it is safe to handle interrupts.
+	 */
 	drv_data->suspended = false;
 
 	/* Start the queue running */
@@ -1561,10 +1644,14 @@ static int pxa2xx_spi_resume(struct device *dev)
 		drv_data->suspended = true;
 		synchronize_irq(ssp->irq);
 		pxa2xx_spi_clk_disable(drv_data);
-		return status;
+		goto out_put;
 	}
 
-	return 0;
+out_put:
+	if (!pm_runtime_suspended(dev))
+		pm_runtime_put_noidle(dev);
+
+	return status;
 }
 
 static int pxa2xx_spi_runtime_suspend(struct device *dev)
diff --git a/drivers/spi/spi-pxa2xx.h b/drivers/spi/spi-pxa2xx.h
index 44f37bf9c519..48169494f74e 100644
--- a/drivers/spi/spi-pxa2xx.h
+++ b/drivers/spi/spi-pxa2xx.h
@@ -71,6 +71,7 @@ struct driver_data {
 	irqreturn_t (*transfer_handler)(struct driver_data *drv_data);
 
 	void __iomem *lpss_base;
+	u32 lpss_priv_ctx[6];
 
 	bool suspended;
 	bool clk_enabled;
-- 
2.39.5