kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 201 insertions, 0 deletions

diff --git a/drivers/bcma/driver_pcie2.c b/drivers/bcma/driver_pcie2.c
new file mode 100644
index 000000000..cf889fc62
--- /dev/null
+++ b/drivers/bcma/driver_pcie2.c
@@ -0,0 +1,201 @@
+/*
+ * Broadcom specific AMBA
+ * PCIe Gen 2 Core
+ *
+ * Copyright 2014, Broadcom Corporation
+ * Copyright 2014, Rafał Miłecki <zajec5@gmail.com>
+ *
+ * Licensed under the GNU/GPL. See COPYING for details.
+ */
+
+#include "bcma_private.h"
+#include <linux/bcma/bcma.h>
+#include <linux/pci.h>
+
+/**************************************************
+ * R/W ops.
+ **************************************************/
+
+#if 0
+static u32 bcma_core_pcie2_cfg_read(struct bcma_drv_pcie2 *pcie2, u32 addr)
+{
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR, addr);
+	pcie2_read32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR);
+	return pcie2_read32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA);
+}
+#endif
+
+static void bcma_core_pcie2_cfg_write(struct bcma_drv_pcie2 *pcie2, u32 addr,
+				      u32 val)
+{
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR, addr);
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA, val);
+}
+
+/**************************************************
+ * Init.
+ **************************************************/
+
+static u32 bcma_core_pcie2_war_delay_perst_enab(struct bcma_drv_pcie2 *pcie2,
+						bool enable)
+{
+	u32 val;
+
+	/* restore back to default */
+	val = pcie2_read32(pcie2, BCMA_CORE_PCIE2_CLK_CONTROL);
+	val |= PCIE2_CLKC_DLYPERST;
+	val &= ~PCIE2_CLKC_DISSPROMLD;
+	if (enable) {
+		val &= ~PCIE2_CLKC_DLYPERST;
+		val |= PCIE2_CLKC_DISSPROMLD;
+	}
+	pcie2_write32(pcie2, (BCMA_CORE_PCIE2_CLK_CONTROL), val);
+	/* flush */
+	return pcie2_read32(pcie2, BCMA_CORE_PCIE2_CLK_CONTROL);
+}
+
+static void bcma_core_pcie2_set_ltr_vals(struct bcma_drv_pcie2 *pcie2)
+{
+	/* LTR0 */
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR, 0x844);
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA, 0x883c883c);
+	/* LTR1 */
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR, 0x848);
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA, 0x88648864);
+	/* LTR2 */
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR, 0x84C);
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA, 0x90039003);
+}
+
+static void bcma_core_pcie2_hw_ltr_war(struct bcma_drv_pcie2 *pcie2)
+{
+	u8 core_rev = pcie2->core->id.rev;
+	u32 devstsctr2;
+
+	if (core_rev < 2 || core_rev == 10 || core_rev > 13)
+		return;
+
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR,
+		      PCIE2_CAP_DEVSTSCTRL2_OFFSET);
+	devstsctr2 = pcie2_read32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA);
+	if (devstsctr2 & PCIE2_CAP_DEVSTSCTRL2_LTRENAB) {
+		/* force the right LTR values */
+		bcma_core_pcie2_set_ltr_vals(pcie2);
+
+		/* TODO:
+		 *si_core_wrapperreg(pcie2, 3, 0x60, 0x8080, 0);
+		 */
+
+		/* enable the LTR */
+		devstsctr2 |= PCIE2_CAP_DEVSTSCTRL2_LTRENAB;
+		pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR,
+			      PCIE2_CAP_DEVSTSCTRL2_OFFSET);
+		pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA, devstsctr2);
+
+		/* set the LTR state to be active */
+		pcie2_write32(pcie2, BCMA_CORE_PCIE2_LTR_STATE,
+			      PCIE2_LTR_ACTIVE);
+		usleep_range(1000, 2000);
+
+		/* set the LTR state to be sleep */
+		pcie2_write32(pcie2, BCMA_CORE_PCIE2_LTR_STATE,
+			      PCIE2_LTR_SLEEP);
+		usleep_range(1000, 2000);
+	}
+}
+
+static void pciedev_crwlpciegen2(struct bcma_drv_pcie2 *pcie2)
+{
+	u8 core_rev = pcie2->core->id.rev;
+	bool pciewar160, pciewar162;
+
+	pciewar160 = core_rev == 7 || core_rev == 9 || core_rev == 11;
+	pciewar162 = core_rev == 5 || core_rev == 7 || core_rev == 8 ||
+		     core_rev == 9 || core_rev == 11;
+
+	if (!pciewar160 && !pciewar162)
+		return;
+
+/* TODO */
+#if 0
+	pcie2_set32(pcie2, BCMA_CORE_PCIE2_CLK_CONTROL,
+		    PCIE_DISABLE_L1CLK_GATING);
+#if 0
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR,
+		      PCIEGEN2_COE_PVT_TL_CTRL_0);
+	pcie2_mask32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA,
+		     ~(1 << COE_PVT_TL_CTRL_0_PM_DIS_L1_REENTRY_BIT));
+#endif
+#endif
+}
+
+static void pciedev_crwlpciegen2_180(struct bcma_drv_pcie2 *pcie2)
+{
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR, PCIE2_PMCR_REFUP);
+	pcie2_set32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA, 0x1f);
+}
+
+static void pciedev_crwlpciegen2_182(struct bcma_drv_pcie2 *pcie2)
+{
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR, PCIE2_SBMBX);
+	pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA, 1 << 0);
+}
+
+static void pciedev_reg_pm_clk_period(struct bcma_drv_pcie2 *pcie2)
+{
+	struct bcma_drv_cc *drv_cc = &pcie2->core->bus->drv_cc;
+	u8 core_rev = pcie2->core->id.rev;
+	u32 alp_khz, pm_value;
+
+	if (core_rev <= 13) {
+		alp_khz = bcma_pmu_get_alp_clock(drv_cc) / 1000;
+		pm_value = (1000000 * 2) / alp_khz;
+		pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDADDR,
+			      PCIE2_PVT_REG_PM_CLK_PERIOD);
+		pcie2_write32(pcie2, BCMA_CORE_PCIE2_CONFIGINDDATA, pm_value);
+	}
+}
+
+void bcma_core_pcie2_init(struct bcma_drv_pcie2 *pcie2)
+{
+	struct bcma_bus *bus = pcie2->core->bus;
+	struct bcma_chipinfo *ci = &bus->chipinfo;
+	u32 tmp;
+
+	tmp = pcie2_read32(pcie2, BCMA_CORE_PCIE2_SPROM(54));
+	if ((tmp & 0xe) >> 1 == 2)
+		bcma_core_pcie2_cfg_write(pcie2, 0x4e0, 0x17);
+
+	switch (bus->chipinfo.id) {
+	case BCMA_CHIP_ID_BCM4360:
+	case BCMA_CHIP_ID_BCM4352:
+		pcie2->reqsize = 1024;
+		break;
+	default:
+		pcie2->reqsize = 128;
+		break;
+	}
+
+	if (ci->id == BCMA_CHIP_ID_BCM4360 && ci->rev > 3)
+		bcma_core_pcie2_war_delay_perst_enab(pcie2, true);
+	bcma_core_pcie2_hw_ltr_war(pcie2);
+	pciedev_crwlpciegen2(pcie2);
+	pciedev_reg_pm_clk_period(pcie2);
+	pciedev_crwlpciegen2_180(pcie2);
+	pciedev_crwlpciegen2_182(pcie2);
+}
+
+/**************************************************
+ * Runtime ops.
+ **************************************************/
+
+void bcma_core_pcie2_up(struct bcma_drv_pcie2 *pcie2)
+{
+	struct bcma_bus *bus = pcie2->core->bus;
+	struct pci_dev *dev = bus->host_pci;
+	int err;
+
+	err = pcie_set_readrq(dev, pcie2->reqsize);
+	if (err)
+		bcma_err(bus, "Error setting PCI_EXP_DEVCTL_READRQ: %d\n", err);
+}