Re: [PATCH] Revert "cxl/port: Enable the HDM decoder capability for switch ports"

On Thu, 15 Jun 2023 16:37:04 -0700 Dave Jiang dave.jiang@intel.com wrote:

On 6/15/23 12:53, Dan Williams wrote:

...

commit eb0764b822b9 ("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: eb0764b822b9 ("cxl/port: Enable the HDM decoder capability for switch ports") Signed-off-by: Dan Williams dan.j.williams@intel.com

Reviewed-by: Dave Jiang dave.jiang@intel.com

Reviewed-by: Jonathan Cameron Jonathan.Cameron@huawei.com

Note we also dropped the 'fix' from the QEMU emulation.

Thanks,

Jonathan

...

---

drivers/cxl/core/pci.c | 27 ++++----------------------- drivers/cxl/cxl.h | 1 - drivers/cxl/port.c | 14 +++++--------- tools/testing/cxl/Kbuild | 1 - tools/testing/cxl/test/mock.c | 15 --------------- 5 files changed, 9 insertions(+), 49 deletions(-)

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c index 7440f84be6c8..552203c13b39 100644 --- a/drivers/cxl/core/pci.c +++ b/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;

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h index 74548f8f5f4c..d743df66a582 100644 --- a/drivers/cxl/cxl.h +++ b/drivers/cxl/cxl.h @@ -717,7 +717,6 @@ 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); diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c index 5ffe3c7d2f5e..43718d0396d7 100644 --- a/drivers/cxl/port.c +++ b/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); }

diff --git a/tools/testing/cxl/Kbuild b/tools/testing/cxl/Kbuild index 6f9347ade82c..fba7bec96acd 100644 --- a/tools/testing/cxl/Kbuild +++ b/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 diff --git a/tools/testing/cxl/test/mock.c b/tools/testing/cxl/test/mock.c index 284416527644..de3933a776fd 100644 --- a/tools/testing/cxl/test/mock.c +++ b/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;