[PATCH 1/2] spi: pxa2xx: disable DMA and fix runtime PM for Apple MacBook8,1

[Shih-Yuan Lee <fourdollars@debian.org>]

On MacBook8,1 (early 2015 12" MacBook), the LPSS SPI controller at
00:15.4 has two related problems:

1. The DMA handshake and interrupt routing frequently fail or time out,
   causing the keyboard and trackpad (driven by the applespi driver via
   SPI) to become unresponsive.  Force PIO mode to avoid this.

2. When DMA is disabled, pm_runtime_allow() must not be called for the
   controller, because runtime autosuspend clock-gates the LPSS block
   between transfers.  Accessing its MMIO registers while clock-gated
   triggers a PCIe Completion Timeout which causes a watchdog reset.

Move the force-PIO quirk to spi-pxa2xx-pci.c (the LPSS host controller
driver) to avoid layering violations in the client driver, and guard
pm_runtime_allow() with the same pxa2xx_spi_pci_can_dma() check used
to set enable_dma so that PIO-mode controllers stay permanently active.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=108331
Signed-off-by: Shih-Yuan Lee <fourdollars@debian.org>
---
 drivers/spi/spi-pxa2xx-pci.c | 38 +++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi-pxa2xx-pci.c b/drivers/spi/spi-pxa2xx-pci.c
index cae77ac18520..cb61f1d2d9e6 100644
--- a/drivers/spi/spi-pxa2xx-pci.c
+++ b/drivers/spi/spi-pxa2xx-pci.c
@@ -18,9 +18,14 @@
 
 #include <linux/dmaengine.h>
 #include <linux/platform_data/dma-dw.h>
+#include <linux/dmi.h>
 
 #include "spi-pxa2xx.h"
 
+static bool spi_pxa2xx_force_pio;
+module_param_named(force_pio, spi_pxa2xx_force_pio, bool, 0444);
+MODULE_PARM_DESC(force_pio, "Force PIO mode (disables DMA) for SPI transfers. ([0] = disabled, 1 = enabled)");
+
 #define PCI_DEVICE_ID_INTEL_QUARK_X1000		0x0935
 #define PCI_DEVICE_ID_INTEL_BYT			0x0f0e
 #define PCI_DEVICE_ID_INTEL_MRFLD		0x1194
@@ -93,6 +98,32 @@ static void lpss_dma_put_device(void *dma_dev)
 	pci_dev_put(dma_dev);
 }
 
+static const struct dmi_system_id pxa2xx_spi_pci_dmi_table[] = {
+	{
+		.ident = "Apple MacBook8,1",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
+			DMI_MATCH(DMI_PRODUCT_NAME, "MacBook8,1"),
+		},
+	},
+	{ }
+};
+
+static bool pxa2xx_spi_pci_can_dma(struct pci_dev *dev)
+{
+	if (spi_pxa2xx_force_pio) {
+		pci_info(dev, "Forcing PIO mode (disabling DMA)\n");
+		return false;
+	}
+
+	if (dmi_check_system(pxa2xx_spi_pci_dmi_table)) {
+		pci_info(dev, "MacBook8,1 detected: disabling DMA to force PIO mode\n");
+		return false;
+	}
+
+	return true;
+}
+
 static int lpss_spi_setup(struct pci_dev *dev, struct pxa2xx_spi_controller *c)
 {
 	struct ssp_device *ssp = &c->ssp;
@@ -166,7 +197,7 @@ static int lpss_spi_setup(struct pci_dev *dev, struct pxa2xx_spi_controller *c)
 
 	c->dma_filter = lpss_dma_filter;
 	c->dma_burst_size = 1;
-	c->enable_dma = 1;
+	c->enable_dma = pxa2xx_spi_pci_can_dma(dev);
 	return 0;
 }
 
@@ -238,7 +269,7 @@ static int mrfld_spi_setup(struct pci_dev *dev, struct pxa2xx_spi_controller *c)
 
 	c->dma_filter = lpss_dma_filter;
 	c->dma_burst_size = 8;
-	c->enable_dma = 1;
+	c->enable_dma = pxa2xx_spi_pci_can_dma(dev);
 	return 0;
 }
 
@@ -303,7 +334,8 @@ static int pxa2xx_spi_pci_probe(struct pci_dev *dev,
 	pm_runtime_set_autosuspend_delay(&dev->dev, 50);
 	pm_runtime_use_autosuspend(&dev->dev);
 	pm_runtime_put_autosuspend(&dev->dev);
-	pm_runtime_allow(&dev->dev);
+	if (pxa2xx_spi_pci_can_dma(dev))
+		pm_runtime_allow(&dev->dev);
 
 	return 0;
 }
-- 
2.39.5