[PATCH v2 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, DDR frequency scaling, 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; DDR
DVFS is left at service level because its reg1 is a frequency setpoint
rather than a fixed subfunction id, and the SoC info call is a read-only
query.  CPU frequency scaling is denied because the hardware domain
cannot make an informed decision, and any unknown function ID is
rejected.

Signed-off-by: Wig Cheng <onlywig@gmail.com>
---
 xen/arch/arm/platforms/Makefile |   1 +
 xen/arch/arm/platforms/imx8m.c  | 152 ++++++++++++++++++++++++++++++++
 2 files changed, 153 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..fcf01298d8
--- /dev/null
+++ b/xen/arch/arm/platforms/imx8m.c
@@ -0,0 +1,152 @@
+/* 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/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
+#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_START     0x00
+#define IMX_SIP_SRC_SF_M4_STOP      0x02
+
+#define IMX_SIP_NOC_SF_LCDIF        0x00
+#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, DRAM controller, 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 )
+            goto deny_subfunction;
+        break;
+
+    case IMX_SIP_FID(IMX_SIP_F_SRC):
+        if ( subfunction_id > IMX_SIP_SRC_SF_M4_STOP )
+            goto deny_subfunction;
+        break;
+
+    case IMX_SIP_FID(IMX_SIP_F_NOC):
+        if ( subfunction_id > IMX_SIP_NOC_SF_PRIORITY )
+            goto deny_subfunction;
+        break;
+
+    case IMX_SIP_FID(IMX_SIP_F_DDR_DVFS):
+        /*
+         * For DDR DVFS reg1 is a frequency setpoint index (or the
+         * GET_FREQ_COUNT / GET_FREQ_INFO query), not a fixed subfunction
+         * id, so it is not filtered here.
+         */
+        break;
+
+    case IMX_SIP_FID(IMX_SIP_F_SOC_INFO):
+        break;
+
+    /*
+     * CPU frequency scaling: the hardware domain does not see the whole
+     * system and cannot make an informed decision, so deny it (matches
+     * the i.MX8QM platform).
+     */
+    case IMX_SIP_FID(IMX_SIP_F_CPUFREQ):
+        return false;
+
+    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;
+
+ deny_subfunction:
+    gprintk(XENLOG_WARNING,
+            "imx8m: smc: function %x: denied subfunction %x\n",
+            function_id, subfunction_id);
+    return false;
+}
+
+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