media: cx23885: only reset DMA on problematic CPUs

It is reported that commit 95f408bb ("media: cx23885: Ryzen DMA
related RiSC engine stall fixes") caused regresssions with other CPUs.

Ensure that the quirk will be applied only for the CPUs that
are known to cause problems.

A module option is added for explicit control of the behaviour.

Fixes: 95f408bb ("media: cx23885: Ryzen DMA related RiSC engine stall fixes")
Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/pci/cx23885/cx23885-core.c

@@ -23,6 +23,7 @@
 #include <linux/moduleparam.h>
 #include <linux/kmod.h>
 #include <linux/kernel.h>
+#include <linux/pci.h>
 #include <linux/slab.h>
 #include <linux/interrupt.h>
 #include <linux/delay.h>
@@ -41,6 +42,18 @@ MODULE_AUTHOR("Steven Toth <stoth@linuxtv.org>");
 MODULE_LICENSE("GPL");
 MODULE_VERSION(CX23885_VERSION);
 
+/*
+ * Some platforms have been found to require periodic resetting of the DMA
+ * engine. Ryzen and XEON platforms are known to be affected. The symptom
+ * encountered is "mpeg risc op code error". Only Ryzen platforms employ
+ * this workaround if the option equals 1. The workaround can be explicitly
+ * disabled for all platforms by setting to 0, the workaround can be forced
+ * on for any platform by setting to 2.
+ */
+static unsigned int dma_reset_workaround = 1;
+module_param(dma_reset_workaround, int, 0644);
+MODULE_PARM_DESC(dma_reset_workaround, "periodic RiSC dma engine reset; 0-force disable, 1-driver detect (default), 2-force enable");
+
 static unsigned int debug;
 module_param(debug, int, 0644);
 MODULE_PARM_DESC(debug, "enable debug messages");
@@ -603,8 +616,13 @@ static void cx23885_risc_disasm(struct cx23885_tsport *port,
 
 static void cx23885_clear_bridge_error(struct cx23885_dev *dev)
 {
-	uint32_t reg1_val = cx_read(TC_REQ); /* read-only */
-	uint32_t reg2_val = cx_read(TC_REQ_SET);
+	uint32_t reg1_val, reg2_val;
+
+	if (!dev->need_dma_reset)
+		return;
+
+	reg1_val = cx_read(TC_REQ); /* read-only */
+	reg2_val = cx_read(TC_REQ_SET);
 
 	if (reg1_val && reg2_val) {
 		cx_write(TC_REQ, reg1_val);
@@ -2058,6 +2076,37 @@ void cx23885_gpio_enable(struct cx23885_dev *dev, u32 mask, int asoutput)
 	/* TODO: 23-19 */
 }
 
+static struct {
+	int vendor, dev;
+} const broken_dev_id[] = {
+	/* According with
+	 * https://openbenchmarking.org/system/1703021-RI-AMDZEN08075/Ryzen%207%201800X/lspci,
+	 * 0x1451 is PCI ID for the IOMMU found on Ryzen
+	 */
+	{ PCI_VENDOR_ID_AMD, 0x1451 },
+};
+
+static bool cx23885_does_need_dma_reset(void)
+{
+	int i;
+	struct pci_dev *pdev = NULL;
+
+	if (dma_reset_workaround == 0)
+		return false;
+	else if (dma_reset_workaround == 2)
+		return true;
+
+	for (i = 0; i < ARRAY_SIZE(broken_dev_id); i++) {
+		pdev = pci_get_device(broken_dev_id[i].vendor,
+				      broken_dev_id[i].dev, NULL);
+		if (pdev) {
+			pci_dev_put(pdev);
+			return true;
+		}
+	}
+	return false;
+}
+
 static int cx23885_initdev(struct pci_dev *pci_dev,
 			   const struct pci_device_id *pci_id)
 {
@@ -2069,6 +2118,8 @@ static int cx23885_initdev(struct pci_dev *pci_dev,
 	if (NULL == dev)
 		return -ENOMEM;
 
+	dev->need_dma_reset = cx23885_does_need_dma_reset();
+
 	err = v4l2_device_register(&pci_dev->dev, &dev->v4l2_dev);
 	if (err < 0)
 		goto fail_free;

drivers/media/pci/cx23885/cx23885.h

@@ -451,6 +451,8 @@ struct cx23885_dev {
 	/* Analog raw audio */
 	struct cx23885_audio_dev   *audio_dev;
 
+	/* Does the system require periodic DMA resets? */
+	unsigned int		need_dma_reset:1;
 };
 
 static inline struct cx23885_dev *to_cx23885(struct v4l2_device *v4l2_dev)