Revert "cxl/port: Enable the HDM decoder capability for switch ports"

commit eb0764b ("cxl/port: Enable the HDM decoder capability for switch ports")

...was added on the observation of CXL memory not being accessible after
setting up a region on a "cold-plugged" device. A "cold-plugged" CXL
device is one that was not present at boot, so platform-firmware/BIOS
has no chance to set it up.

While it is true that the debug found the enable bit clear in the
host-bridge's instance of the global control register (CXL 3.0
8.2.4.19.2 CXL HDM Decoder Global Control Register), that bit is
described as:

"This bit is only applicable to CXL.mem devices and shall
return 0 on CXL Host Bridges and Upstream Switch Ports."

So it is meant to be zero, and further testing confirmed that this "fix"
had no effect on the failure. Revert it, and be more vigilant about
proposed fixes in the future. Since the original copied stable@, flag
this revert for stable@ as well.

Cc: <stable@vger.kernel.org>
Fixes: eb0764b ("cxl/port: Enable the HDM decoder capability for switch ports")
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/168685882012.3475336.16733084892658264991.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Author: djbw

drivers/cxl/core/pci.c

@@ -308,36 +308,17 @@ static void disable_hdm(void *_cxlhdm)
 	       hdm + CXL_HDM_DECODER_CTRL_OFFSET);
 }
 
-int devm_cxl_enable_hdm(struct cxl_port *port, struct cxl_hdm *cxlhdm)
+static int devm_cxl_enable_hdm(struct device *host, struct cxl_hdm *cxlhdm)
 {
-	void __iomem *hdm;
+	void __iomem *hdm = cxlhdm->regs.hdm_decoder;
 	u32 global_ctrl;
 
-	/*
-	 * If the hdm capability was not mapped there is nothing to enable and
-	 * the caller is responsible for what happens next.  For example,
-	 * emulate a passthrough decoder.
-	 */
-	if (IS_ERR(cxlhdm))
-		return 0;
-
-	hdm = cxlhdm->regs.hdm_decoder;
 	global_ctrl = readl(hdm + CXL_HDM_DECODER_CTRL_OFFSET);
-
-	/*
-	 * If the HDM decoder capability was enabled on entry, skip
-	 * registering disable_hdm() since this decode capability may be
-	 * owned by platform firmware.
-	 */
-	if (global_ctrl & CXL_HDM_DECODER_ENABLE)
-		return 0;
-
 	writel(global_ctrl | CXL_HDM_DECODER_ENABLE,
 	       hdm + CXL_HDM_DECODER_CTRL_OFFSET);
 
-	return devm_add_action_or_reset(&port->dev, disable_hdm, cxlhdm);
+	return devm_add_action_or_reset(host, disable_hdm, cxlhdm);
 }
-EXPORT_SYMBOL_NS_GPL(devm_cxl_enable_hdm, CXL);
 
 int cxl_dvsec_rr_decode(struct device *dev, int d,
 			struct cxl_endpoint_dvsec_info *info)
@@ -511,7 +492,7 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
 	if (info->mem_enabled)
 		return 0;
 
-	rc = devm_cxl_enable_hdm(port, cxlhdm);
+	rc = devm_cxl_enable_hdm(&port->dev, cxlhdm);
 	if (rc)
 		return rc;
 

drivers/cxl/cxl.h

@@ -710,7 +710,6 @@ struct cxl_endpoint_dvsec_info {
 struct cxl_hdm;
 struct cxl_hdm *devm_cxl_setup_hdm(struct cxl_port *port,
 				   struct cxl_endpoint_dvsec_info *info);
-int devm_cxl_enable_hdm(struct cxl_port *port, struct cxl_hdm *cxlhdm);
 int devm_cxl_enumerate_decoders(struct cxl_hdm *cxlhdm,
 				struct cxl_endpoint_dvsec_info *info);
 int devm_cxl_add_passthrough_decoder(struct cxl_port *port);

drivers/cxl/port.c

@@ -60,17 +60,13 @@ static int discover_region(struct device *dev, void *root)
 static int cxl_switch_port_probe(struct cxl_port *port)
 {
 	struct cxl_hdm *cxlhdm;
-	int rc, nr_dports;
-
-	nr_dports = devm_cxl_port_enumerate_dports(port);
-	if (nr_dports < 0)
-		return nr_dports;
+	int rc;
 
-	cxlhdm = devm_cxl_setup_hdm(port, NULL);
-	rc = devm_cxl_enable_hdm(port, cxlhdm);
-	if (rc)
+	rc = devm_cxl_port_enumerate_dports(port);
+	if (rc < 0)
 		return rc;
 
+	cxlhdm = devm_cxl_setup_hdm(port, NULL);
 	if (!IS_ERR(cxlhdm))
 		return devm_cxl_enumerate_decoders(cxlhdm, NULL);
 
@@ -79,7 +75,7 @@ static int cxl_switch_port_probe(struct cxl_port *port)
 		return PTR_ERR(cxlhdm);
 	}
 
-	if (nr_dports == 1) {
+	if (rc == 1) {
 		dev_dbg(&port->dev, "Fallback to passthrough decoder\n");
 		return devm_cxl_add_passthrough_decoder(port);
 	}

tools/testing/cxl/Kbuild

@@ -6,7 +6,6 @@ ldflags-y += --wrap=acpi_pci_find_root
 ldflags-y += --wrap=nvdimm_bus_register
 ldflags-y += --wrap=devm_cxl_port_enumerate_dports
 ldflags-y += --wrap=devm_cxl_setup_hdm
-ldflags-y += --wrap=devm_cxl_enable_hdm
 ldflags-y += --wrap=devm_cxl_add_passthrough_decoder
 ldflags-y += --wrap=devm_cxl_enumerate_decoders
 ldflags-y += --wrap=cxl_await_media_ready

tools/testing/cxl/test/mock.c

@@ -149,21 +149,6 @@ struct cxl_hdm *__wrap_devm_cxl_setup_hdm(struct cxl_port *port,
 }
 EXPORT_SYMBOL_NS_GPL(__wrap_devm_cxl_setup_hdm, CXL);
 
-int __wrap_devm_cxl_enable_hdm(struct cxl_port *port, struct cxl_hdm *cxlhdm)
-{
-	int index, rc;
-	struct cxl_mock_ops *ops = get_cxl_mock_ops(&index);
-
-	if (ops && ops->is_mock_port(port->uport))
-		rc = 0;
-	else
-		rc = devm_cxl_enable_hdm(port, cxlhdm);
-	put_cxl_mock_ops(index);
-
-	return rc;
-}
-EXPORT_SYMBOL_NS_GPL(__wrap_devm_cxl_enable_hdm, CXL);
-
 int __wrap_devm_cxl_add_passthrough_decoder(struct cxl_port *port)
 {
 	int rc, index;