[PATCH] spi: atmel-quadspi: balance runtime PM and pclk across system sleep

[Karl Mehltretter <kmehltretter@gmail.com>]

On the controllers with a generic clock (SAMA7G5, SAMA7D65, SAM9X7 and
LAN969x), atmel_qspi_suspend() takes a runtime PM reference and returns
without dropping it or suspending the device. It disables the peripheral
clock directly. atmel_qspi_resume() only prepares the peripheral clock
and then reinitializes the controller with that clock still off.

On a SAM9X75 Curiosity board, the tested standby and mem resumes
failed:

  atmel_qspi f0014000.spi: PM: failed to resume: error -110
  spi-nor spi0.0: resume() failed

Reading the flash afterwards returned no data. The runtime usage count
grew by one with each cycle, and the second suspend disabled the
peripheral clock again:

  WARNING: drivers/clk/clk.c:1257 at clk_core_disable+0x6c/0xcc
  qspi_clk already disabled

Use the same runtime PM sequence as the other variants. Suspend disables
the controller and forces a runtime suspend. Resume forces a runtime
resume, which enables the peripheral clock, before it runs the init
callback, and drops the reference afterwards. With this change the
tested resumes succeed on the board in both modes, the controller
returns to runtime suspend, and the flash reads back.

Fixes: 5af42209a4d2 ("spi: atmel-quadspi: Add support for sama7g5 QSPI")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260709112006.390742-1-robert.marko%40sartura.hr?part=3
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
---
A/B tested on a SAM9X75 Curiosity board, two real suspend cycles each
in standby and mem, woken by the RTC, with a read of the on-board
SST26VF064B after every resume:

                           without patch          with patch
  resume                   error -110             ok
  runtime status / usage   active / 1, then 2     suspended / 0
  second suspend           WARNING, qspi_clk      clean
                           already disabled
  flash read               no data                matches

pm_test=devices gives the same result. QEMU's sam9x75-curiosity model
shows the same runtime PM and clock state. Its OSPI does not depend on
pclk, so there reads succeed in both cases.

Not tested: SAMA7G5, SAMA7D65 and LAN969x.

Unrelated to this patch: with and without it, each tested OSPI flash
read on SAM9X75 printed "BUG: sleeping function called from invalid
context" from at_xdmac_issue_pending().

 drivers/spi/atmel-quadspi.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/spi/atmel-quadspi.c b/drivers/spi/atmel-quadspi.c
index ec19fa0180f00..96ed734b56218 100644
--- a/drivers/spi/atmel-quadspi.c
+++ b/drivers/spi/atmel-quadspi.c
@@ -1590,12 +1590,14 @@ static int atmel_qspi_suspend(struct device *dev)
 
 	if (aq->caps->has_gclk) {
 		ret = atmel_qspi_sama7g5_suspend(aq);
-		clk_disable_unprepare(aq->pclk);
-		return ret;
+		if (ret) {
+			pm_runtime_put_autosuspend(dev);
+			return ret;
+		}
+	} else {
+		atmel_qspi_write(QSPI_CR_QSPIDIS, aq, QSPI_CR);
 	}
 
-	atmel_qspi_write(QSPI_CR_QSPIDIS, aq, QSPI_CR);
-
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_force_suspend(dev);
 
@@ -1621,20 +1623,20 @@ static int atmel_qspi_resume(struct device *dev)
 		return ret;
 	}
 
-	if (aq->caps->has_gclk)
-		return aq->caps->init(aq);
-
 	ret = pm_runtime_force_resume(dev);
 	if (ret < 0)
 		return ret;
 
-	atmel_qspi_init(aq);
-
-	atmel_qspi_write(aq->scr, aq, QSPI_SCR);
+	if (aq->caps->has_gclk) {
+		ret = aq->caps->init(aq);
+	} else {
+		atmel_qspi_init(aq);
+		atmel_qspi_write(aq->scr, aq, QSPI_SCR);
+	}
 
 	pm_runtime_put_autosuspend(dev);
 
-	return 0;
+	return ret;
 }
 
 static int atmel_qspi_runtime_suspend(struct device *dev)
-- 
2.53.0