cxl: Check if PSL data-cache is available before issue flush request

PSL9D doesn't have a data-cache that needs to be flushed before
resetting the card. However when cxl tries to flush data-cache on such
a card, it times-out as PSL_Control register never indicates flush
operation complete due to missing data-cache. This is usually
indicated in the kernel logs with this message:

"WARNING: cache flush timed out"

To fix this the patch checks PSL_Debug register CDC-Field(BIT:27)
which indicates the absence of a data-cache and sets a flag
'no_data_cache' in 'struct cxl_native' to indicate this. When
cxl_data_cache_flush() is called it checks the flag and if set bails
out early without requesting a data-cache flush operation to the PSL.

Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/cxl.h

@@ -369,6 +369,9 @@ static const cxl_p2n_reg_t CXL_PSL_WED_An     = {0x0A0};
 #define CXL_PSL_TFC_An_AE (1ull << (63-30)) /* Restart PSL with address error */
 #define CXL_PSL_TFC_An_R  (1ull << (63-31)) /* Restart PSL transaction */
 
+/****** CXL_PSL_DEBUG *****************************************************/
+#define CXL_PSL_DEBUG_CDC  (1ull << (63-27)) /* Coherent Data cache support */
+
 /****** CXL_XSL9_IERAT_ERAT - CAIA 2 **********************************/
 #define CXL_XSL9_IERAT_MLPID    (1ull << (63-0))  /* Match LPID */
 #define CXL_XSL9_IERAT_MPID     (1ull << (63-1))  /* Match PID */
@@ -669,6 +672,7 @@ struct cxl_native {
 	irq_hw_number_t err_hwirq;
 	unsigned int err_virq;
 	u64 ps_off;
+	bool no_data_cache; /* set if no data cache on the card */
 	const struct cxl_service_layer_ops *sl_ops;
 };
 

drivers/misc/cxl/native.c

@@ -353,8 +353,17 @@ int cxl_data_cache_flush(struct cxl *adapter)
 	u64 reg;
 	unsigned long timeout = jiffies + (HZ * CXL_TIMEOUT);
 
-	pr_devel("Flushing data cache\n");
+	/*
+	 * Do a datacache flush only if datacache is available.
+	 * In case of PSL9D datacache absent hence flush operation.
+	 * would timeout.
+	 */
+	if (adapter->native->no_data_cache) {
+		pr_devel("No PSL data cache. Ignoring cache flush req.\n");
+		return 0;
+	}
 
+	pr_devel("Flushing data cache\n");
 	reg = cxl_p1_read(adapter, CXL_PSL_Control);
 	reg |= CXL_PSL_Control_Fr;
 	cxl_p1_write(adapter, CXL_PSL_Control, reg);

drivers/misc/cxl/pci.c

@@ -456,6 +456,7 @@ static int init_implementation_adapter_regs_psl9(struct cxl *adapter,
 	u64 chipid;
 	u32 phb_index;
 	u64 capp_unit_id;
+	u64 psl_debug;
 	int rc;
 
 	rc = cxl_calc_capp_routing(dev, &chipid, &phb_index, &capp_unit_id);
@@ -510,6 +511,16 @@ static int init_implementation_adapter_regs_psl9(struct cxl *adapter,
 		cxl_p1_write(adapter, CXL_PSL9_DEBUG, 0xC000000000000000ULL);
 	}
 
+	/*
+	 * Check if PSL has data-cache. We need to flush adapter datacache
+	 * when as its about to be removed.
+	 */
+	psl_debug = cxl_p1_read(adapter, CXL_PSL9_DEBUG);
+	if (psl_debug & CXL_PSL_DEBUG_CDC) {
+		dev_dbg(&dev->dev, "No data-cache present\n");
+		adapter->native->no_data_cache = true;
+	}
+
 	return 0;
 }
 
@@ -1448,10 +1459,8 @@ int cxl_pci_reset(struct cxl *adapter)
 
 	/*
 	 * The adapter is about to be reset, so ignore errors.
-	 * Not supported on P9 DD1
 	 */
-	if ((cxl_is_power8()) || (!(cxl_is_power9_dd1())))
-		cxl_data_cache_flush(adapter);
+	cxl_data_cache_flush(adapter);
 
 	/* pcie_warm_reset requests a fundamental pci reset which includes a
 	 * PERST assert/deassert.  PERST triggers a loading of the image
@@ -1934,10 +1943,8 @@ static void cxl_pci_remove_adapter(struct cxl *adapter)
 
 	/*
 	 * Flush adapter datacache as its about to be removed.
-	 * Not supported on P9 DD1.
 	 */
-	if ((cxl_is_power8()) || (!(cxl_is_power9_dd1())))
-		cxl_data_cache_flush(adapter);
+	cxl_data_cache_flush(adapter);
 
 	cxl_deconfigure_adapter(adapter);