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

Derick noticed, when testing hot plug, that hot-add behaves nominally
after a removal. However, if the hot-add is done without a prior
removal, CXL.mem accesses fail. It turns out that the original
implementation of the port driver and region programming wrongly assumed
that platform-firmware always enables the host-bridge HDM decoder
capability. Add support turning on switch-level HDM decoders in the case
where platform-firmware has not.

The implementation is careful to only arrange for the enable to be
undone if the current instance of the driver was the one that did the
enable. This is to interoperate with platform-firmware that may expect
CXL.mem to remain active after the driver is shutdown. This comes at the
cost of potentially not shutting down the enable on kexec flows, but it
is mitigated by the fact that the related HDM decoders still need to be
enabled on an individual basis.

Cc: <stable@vger.kernel.org>
Reported-by: Derick Marks <derick.w.marks@intel.com>
Fixes: 54cdbf845cf7 ("cxl/port: Add a driver for 'struct cxl_port' objects")
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/168437998331.403037.15719879757678389217.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index f332fe7af92ba3f86833ca9f3517723b855e53a2..c35c002b65dd4c16b8bf1280c7e31f6cb93159f9 100644 (file)
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -241,17 +241,36 @@ static void disable_hdm(void *_cxlhdm)
               hdm + CXL_HDM_DECODER_CTRL_OFFSET);
 }
 
-static int devm_cxl_enable_hdm(struct device *host, struct cxl_hdm *cxlhdm)
+int devm_cxl_enable_hdm(struct cxl_port *port, struct cxl_hdm *cxlhdm)
 {
-       void __iomem *hdm = cxlhdm->regs.hdm_decoder;
+       void __iomem *hdm;
        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(host, disable_hdm, cxlhdm);
+       return devm_add_action_or_reset(&port->dev, 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)
@@ -425,7 +444,7 @@ 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->dev, cxlhdm);
+       rc = devm_cxl_enable_hdm(port, cxlhdm);
        if (rc)
                return rc;
 

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 044a92d9813e239d1b97e7a4935f36850c30e154..f93a285389621cc77e86ae792c095b1671f30c85 100644 (file)
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -710,6 +710,7 @@ 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);

diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
index eb57324c4ad4a0e54c9a35500df9c3a216f603a2..17a95f469c262979c4f102e605680d7b52ea1572 100644 (file)
--- a/drivers/cxl/port.c
+++ b/drivers/cxl/port.c
@@ -60,13 +60,17 @@ 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;
+       int rc, nr_dports;
 
-       rc = devm_cxl_port_enumerate_dports(port);
-       if (rc < 0)
-               return rc;
+       nr_dports = devm_cxl_port_enumerate_dports(port);
+       if (nr_dports < 0)
+               return nr_dports;
 
        cxlhdm = devm_cxl_setup_hdm(port, NULL);
+       rc = devm_cxl_enable_hdm(port, cxlhdm);
+       if (rc)
+               return rc;
+
        if (!IS_ERR(cxlhdm))
                return devm_cxl_enumerate_decoders(cxlhdm, NULL);
 
@@ -75,7 +79,7 @@ static int cxl_switch_port_probe(struct cxl_port *port)
                return PTR_ERR(cxlhdm);
        }
 
-       if (rc == 1) {
+       if (nr_dports == 1) {
                dev_dbg(&port->dev, "Fallback to passthrough decoder\n");
                return devm_cxl_add_passthrough_decoder(port);
        }

diff --git a/tools/testing/cxl/Kbuild b/tools/testing/cxl/Kbuild
index fba7bec96acd184297189798d1708ef1e6e2df7e..6f9347ade82cde19fac94be0bea8736192f2ec3b 100644 (file)
--- a/tools/testing/cxl/Kbuild
+++ b/tools/testing/cxl/Kbuild
@@ -6,6 +6,7 @@ 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

diff --git a/tools/testing/cxl/test/mock.c b/tools/testing/cxl/test/mock.c
index de3933a776fdb250b4afc7f135cb0d2cf1d7d0ec..28441652764405d0e2fae9add9c4f7372c15facc 100644 (file)
--- a/tools/testing/cxl/test/mock.c
+++ b/tools/testing/cxl/test/mock.c
@@ -149,6 +149,21 @@ 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;