spi: spi-zynqmp-gqspi: stop the controller on shutdown

The driver has no ->shutdown, and platform_drv_shutdown() has no fallback of its own. Unlike pci_device_shutdown(), which clears bus mastering when kexec_in_progress, nothing on the platform bus disarms a device that can still write to memory. The normal kexec path never calls ->suspend either, so the quiesce in zynqmp_qspi_suspend() is not reached.

A controller that is still executing a DMA read may therefore keep writing to memory across a kexec. QSPIDMA_DST_ADDR still points at memory owned by the kernel that called kexec, DST_SIZE is non-zero and the flash is still clocked, so data can keep landing in RAM while the new kernel is being relocated, and after it has started executing.

That destination is a physical address which means nothing to the new kernel, so the writes can corrupt whatever now occupies it: kernel text or data, page tables, or the initrd. Nothing reports an error and the resulting behaviour is undefined.

This can be observed by reading GQSPI_EN (offset 0x114) and QSPIDMA_DST_ADDR/SIZE/STS/CTRL (offsets 0x800 to 0x80c) early in the new kernel, before the driver probes: without this patch GQSPI_EN reads 1 and QSPIDMA_DST_ADDR still points into the previous kernel's memory.

Add a ->shutdown that stops the controller the way zynqmp_qspi_suspend() already does. spi_controller_suspend() stops the queue, waits for a message that is already executing and makes any later transfer fail with -ESHUTDOWN, so nothing can be cut short by the register write that follows. It may sleep, which is fine here: device_shutdown() runs in process context. Unlike ->suspend this cannot abort on error, because a controller left mastering the bus is worse than a truncated transfer, so a failure to drain is only logged.

GQSPI_EN_OFST is then cleared, as zynqmp_qspi_remove() and zynqmp_qspi_suspend() already do. Skip that write only when pm_runtime_get_if_in_use() returns 0, i.e. runtime suspended: the clocks are gated, so the registers are unreachable and the controller cannot be mastering the bus. A negative return is not the same thing - it is what the CONFIG_PM=n stub always returns, and there probe() has enabled pclk and refclk for good, so the controller is running and must be stopped.

---
Changes in v2:
- Quiesce through spi_controller_suspend() before touching the hardware, so nothing can start a new transfer and a message that is already executing is waited for (Mark Brown).

Note for stable: before commit 1c26372e5aa9 ("spi: spi-zynqmp-gqspi:
Update driver to use spi-mem framework") this driver stored the spi_master in the platform drvdata rather than the zynqmp_qspi, so a backport to those trees needs spi_master_get_devdata() in place of the platform_get_drvdata() used here.

 drivers/spi/spi-zynqmp-gqspi.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

index 4d55090..15e9d3e 100644
@@ -1373,11 +1373,45 @@ static void zynqmp_qspi_remove(struct platform_device *pdev)
 	clk_disable_unprepare(xqspi->pclk);
 }
 
+static void zynqmp_qspi_shutdown(struct platform_device *pdev)
+{
+	struct zynqmp_qspi *xqspi = platform_get_drvdata(pdev);
+	int ret;
+
+	/*
+	 * Stop the queue and reject any later transfer first, so the write
+	 * below cannot cut into a message that is still being executed.
+	 * Unlike ->suspend this cannot abort on error: a controller left
+	 * mastering the bus is worse than a truncated transfer.
+	 */
+	ret = spi_controller_suspend(xqspi->ctlr);
+	if (ret)
+		dev_warn(&pdev->dev, "could not stop the queue: %d\n", ret);
+
+	/*
+	 * Only a runtime suspended controller can be left alone: its clocks
+	 * are gated, so it cannot be mastering the bus, and its registers
+	 * must not be accessed either.  Any other answer means it may be
+	 * running and has to be stopped.  In particular, on a kernel built
+	 * without runtime PM this returns -EINVAL, and there the clocks
+	 * enabled in probe() are never gated at all.
+	 */
+	ret = pm_runtime_get_if_in_use(&pdev->dev);
+	if (!ret)
+		return;
+
+	zynqmp_gqspi_write(xqspi, GQSPI_EN_OFST, 0x0);
+
+	if (ret > 0)
+		pm_runtime_put_noidle(&pdev->dev);
+}
+
 MODULE_DEVICE_TABLE(of, zynqmp_qspi_of_match);
 
 static struct platform_driver zynqmp_qspi_driver = {
 	.probe = zynqmp_qspi_probe,
 	.remove = zynqmp_qspi_remove,
+	.shutdown = zynqmp_qspi_shutdown,
 	.driver = {
 		.name = "zynqmp-qspi",
 		.of_match_table = zynqmp_qspi_of_match,

2.34.1

Applied to

https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-7.3

Thanks!

[1/1] spi: spi-zynqmp-gqspi: stop the controller on shutdown

      https://git.kernel.org/broonie/spi/c/e922bad8b2d5

All being well this means that it will be integrated into the linux-next tree (usually sometime in the next 24 hours) and sent to Linus during the next merge window (or sooner if it is a bug fix), however if problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing and review of the tree, please engage with people reporting problems and send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they should be sent as incremental updates against current git, existing patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying to this mail.

Thanks,
Mark