[PATCH v3 3/4] xen/arm: add i.MX8M platform support

[Wig Cheng <onlywig@gmail.com>]

Add platform glue for the NXP i.MX8M family (i.MX8MP/MQ/MM/MN).

When Linux is used as dom0 a number of drivers make SiP SMC calls into
TF-A to manage hardware: GPC power domains, SRC (M-core remoteproc),
SoC info and NoC QoS.  There is no public specification for these
calls; the function IDs and their subfunctions are taken from the
vendor kernel call sites.

Forward only the specific subfunctions the hardware domain issues,
following the whitelist model of the i.MX8QM platform.  Where a service
has a fixed set of subfunctions (GPC, SRC, NoC) they are filtered, and
the SoC info call is a read-only query.  CPU and DRAM frequency scaling
are denied because the hardware domain cannot make an informed decision
about resources shared with the other domains, and any unknown function
ID is rejected.

Signed-off-by: Wig Cheng <onlywig@gmail.com>
---
Changes in v3:
- Include <asm/regs.h> for get/set_user_reg().
- Add a description for the CPUFREQ function id.
- Drop the unused SRC M4_START and NoC LCDIF subfunction macros.
- Order the switch cases by function id.
- Deny DDR DVFS as well, for the same reason CPU frequency scaling is
  denied: the hardware domain cannot make an informed decision about
  DRAM shared with the other domains.  Previously it was forwarded.
- Return false directly on a denied subfunction instead of goto plus a
  redundant printk (vsmccc_handle_call() already logs the rejection).

 xen/arch/arm/platforms/Makefile |   1 +
 xen/arch/arm/platforms/imx8m.c  | 139 ++++++++++++++++++++++++++++++++
 2 files changed, 140 insertions(+)
 create mode 100644 xen/arch/arm/platforms/imx8m.c

diff --git a/xen/arch/arm/platforms/Makefile b/xen/arch/arm/platforms/Makefile
index bec6e55d1f..cdf936c50d 100644
--- a/xen/arch/arm/platforms/Makefile
+++ b/xen/arch/arm/platforms/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_ALL_PLAT)   += sunxi.o
 obj-$(CONFIG_ALL64_PLAT) += thunderx.o
 obj-$(CONFIG_ALL64_PLAT) += xgene-storm.o
 obj-$(CONFIG_ALL64_PLAT) += brcm-raspberry-pi.o
+obj-$(CONFIG_ALL64_PLAT) += imx8m.o
 obj-$(CONFIG_ALL64_PLAT) += imx8qm.o
 obj-$(CONFIG_MPSOC_PLATFORM)  += xilinx-zynqmp.o
 obj-$(CONFIG_MPSOC_PLATFORM)  += xilinx-zynqmp-eemi.o
diff --git a/xen/arch/arm/platforms/imx8m.c b/xen/arch/arm/platforms/imx8m.c
new file mode 100644
index 0000000000..0aceed9d43
--- /dev/null
+++ b/xen/arch/arm/platforms/imx8m.c
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * i.MX 8M family setup
+ *
+ * Copyright 2026 Open-EP (E-Paper) Community
+ */
+
+#include <xen/sched.h>
+#include <asm/platform.h>
+#include <asm/regs.h>
+#include <asm/smccc.h>
+
+static const char * const imx8m_dt_compat[] __initconst =
+{
+    "fsl,imx8mp",
+    "fsl,imx8mq",
+    "fsl,imx8mm",
+    "fsl,imx8mn",
+    NULL
+};
+
+#define IMX_SIP_FID(fid) \
+    ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \
+                       ARM_SMCCC_CONV_64, \
+                       ARM_SMCCC_OWNER_SIP, \
+                       (fid))
+
+/*
+ * SiP SMC function IDs used by the i.MX8M Linux drivers.  There is no
+ * public specification for these; the IDs and their subfunctions are
+ * extracted from the vendor kernel call sites (see drivers/soc/imx,
+ * drivers/devfreq, drivers/remoteproc).
+ */
+#define IMX_SIP_F_GPC       0x0   /* GPC power-domain control */
+#define IMX_SIP_F_CPUFREQ   0x1   /* CPU frequency scaling */
+#define IMX_SIP_F_DDR_DVFS  0x4   /* DRAM frequency scaling */
+#define IMX_SIP_F_SRC       0x5   /* SRC: M-core remoteproc start/stop */
+#define IMX_SIP_F_SOC_INFO  0x6   /* read-only SoC info query */
+#define IMX_SIP_F_NOC       0x8   /* NoC QoS priority setup */
+
+#define IMX_SIP_GPC_SF_PM_DOMAIN    0x03
+
+#define IMX_SIP_SRC_SF_M4_STOP      0x02
+
+#define IMX_SIP_NOC_SF_PRIORITY     0x01
+
+static bool imx8m_smc(struct cpu_user_regs *regs)
+{
+    uint32_t function_id = get_user_reg(regs, 0);
+    uint32_t subfunction_id = get_user_reg(regs, 1);
+    struct arm_smccc_res res;
+
+    if ( !cpus_have_const_cap(ARM_SMCCC_1_1) )
+    {
+        printk_once(XENLOG_WARNING
+                    "imx8m: smc: no SMCCC 1.1 support. Disabling firmware calls\n");
+
+        return false;
+    }
+
+    /* Only the hardware domain may use the SiP calls */
+    if ( !is_hardware_domain(current->domain) )
+    {
+        gprintk(XENLOG_WARNING, "imx8m: smc: No access\n");
+        return false;
+    }
+
+    /*
+     * Forward only the subfunctions the dom0 kernel actually issues.  All
+     * of these manage hardware that belongs to the hardware domain (power
+     * domains, M-core, NoC) or are read-only queries.
+     */
+    switch ( function_id )
+    {
+    case IMX_SIP_FID(IMX_SIP_F_GPC):
+        if ( subfunction_id != IMX_SIP_GPC_SF_PM_DOMAIN )
+            return false;
+        break;
+
+    /*
+     * CPU and DRAM frequency scaling: the hardware domain does not see the
+     * whole system and cannot make an informed decision about resources
+     * shared with the other domains, so deny both (CPU frequency scaling
+     * is denied on the i.MX8QM platform for the same reason).
+     */
+    case IMX_SIP_FID(IMX_SIP_F_CPUFREQ):
+    case IMX_SIP_FID(IMX_SIP_F_DDR_DVFS):
+        return false;
+
+    case IMX_SIP_FID(IMX_SIP_F_SRC):
+        if ( subfunction_id > IMX_SIP_SRC_SF_M4_STOP )
+            return false;
+        break;
+
+    case IMX_SIP_FID(IMX_SIP_F_SOC_INFO):
+        break;
+
+    case IMX_SIP_FID(IMX_SIP_F_NOC):
+        if ( subfunction_id > IMX_SIP_NOC_SF_PRIORITY )
+            return false;
+        break;
+
+    default:
+        gprintk(XENLOG_WARNING, "imx8m: smc: Unknown function id %x\n",
+                function_id);
+        return false;
+    }
+
+    arm_smccc_1_1_smc(function_id,
+                      subfunction_id,
+                      get_user_reg(regs, 2),
+                      get_user_reg(regs, 3),
+                      get_user_reg(regs, 4),
+                      get_user_reg(regs, 5),
+                      get_user_reg(regs, 6),
+                      get_user_reg(regs, 7),
+                      &res);
+
+    set_user_reg(regs, 0, res.a0);
+    set_user_reg(regs, 1, res.a1);
+    set_user_reg(regs, 2, res.a2);
+    set_user_reg(regs, 3, res.a3);
+
+    return true;
+}
+
+PLATFORM_START(imx8m, "i.MX 8M")
+    .compatible = imx8m_dt_compat,
+    .smc = imx8m_smc,
+PLATFORM_END
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
-- 
2.43.0