[Qemu-devel] [PATCH v4 1/1] pci-host: add educational driver

[Jiri Slaby]

I am using qemu for teaching the Linux kernel at our university. I
wrote a simple PCI device that can answer to writes/reads, generate
interrupts and perform DMA. As I am dragging it locally over 2 years,
I am sending it to you now.

Signed-off-by: Jiri Slaby <address@hidden>
---
 MAINTAINERS             |   5 +
 default-configs/pci.mak |   1 +
 docs/specs/edu.txt      | 106 +++++++++++++
 hw/misc/Makefile.objs   |   1 +
 hw/misc/edu.c           | 401 ++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 514 insertions(+)
 create mode 100644 docs/specs/edu.txt
 create mode 100644 hw/misc/edu.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 430688dcab57..fd335a47bf5c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -599,6 +599,11 @@ F: hw/net/opencores_eth.c
 
 Devices
 -------
+EDU
+M: Jiri Slaby <address@hidden>
+S: Maintained
+F: hw/misc/edu.c
+
 IDE
 M: Kevin Wolf <address@hidden>
 M: Stefan Hajnoczi <address@hidden>
diff --git a/default-configs/pci.mak b/default-configs/pci.mak
index a186c39c0e32..030cdc7d3dd0 100644
--- a/default-configs/pci.mak
+++ b/default-configs/pci.mak
@@ -32,3 +32,4 @@ CONFIG_PCI_TESTDEV=y
 CONFIG_NVME_PCI=y
 CONFIG_SD=y
 CONFIG_SDHCI=y
+CONFIG_EDU=y
diff --git a/docs/specs/edu.txt b/docs/specs/edu.txt
new file mode 100644
index 000000000000..a15d6a2545f0
--- /dev/null
+++ b/docs/specs/edu.txt
@@ -0,0 +1,106 @@
+
+EDU device
+==========
+
+This is an educational device for writing (kernel) drivers. Its original
+intention was to support the Linux kernel lectures taught at the Masaryk
+University. Students are given this virtual device and are expected to write a
+driver with I/Os, IRQs, DMAs and such.
+
+The devices behaves very similar to the PCI bridge present in the COMBO6 cards
+developed under the Liberouter wings. Both PCI device ID and PCI space is
+inherited from that device.
+
+Command line switches:
+    -device edu[,dma_mask=mask]
+
+    dma_mask makes the virtual device work with DMA addresses with the given
+    mask. For educational purposes, the device supports only 28 bits (256 MiB)
+    by default. Students shall set dma_mask for the device in the OS driver
+    properly.
+
+PCI specs
+---------
+
+PCI ID: 1234:11e8
+
+PCI Region 0:
+   I/O memory, 1 MB in size. Users are supposed to communicate with the card
+   through this memory.
+
+MMIO area spec
+--------------
+
+Only size == 4 accesses are allowed for addresses < 0x80. size == 4 or
+size == 8 for the rest.
+
+0x00 (RO) : identification (0xRRrr00edu)
+           RR -- major version
+           rr -- minor version
+
+0x04 (RW) : card liveness check
+           It is a simple value inversion (~ C operator).
+
+0x08 (RW) : factorial computation
+           The stored value is taken and factorial of it is put back here.
+           This happens only after factorial bit in the status register (0x20
+           below) is cleared.
+
+0x20 (RW) : status register, bitwise OR
+           0x01 -- computing factorial (RO)
+           0x02 -- raise interrupt 0x01 after finishing factorial computation
+
+0x24 (RO) : interrupt status register
+           It contains values which raised the interrupt (see interrupt raise
+           register below).
+
+0x60 (WO) : interrupt raise register
+           Raise an interrupt. The value will be put to the interrupt status
+           register (using bitwise OR).
+
+0x64 (WO) : interrupt acknowledge register
+           Clear an interrupt. The value will be cleared from the interrupt
+           status register. This needs to be done from the ISR to stop
+           generating interrupts.
+
+0x80 (RW) : DMA source address
+           Where to perform the DMA from.
+
+0x88 (RW) : DMA destination address
+           Where to perform the DMA to.
+
+0x90 (RW) : DMA transfer count
+           The size of the area to perform the DMA on.
+
+0x98 (RW) : DMA command register, bitwise OR
+           0x01 -- start transfer
+           0x02 -- direction (0: from RAM to EDU, 1: from EDU to RAM)
+           0x04 -- raise interrupt 0x100 after finishing the DMA
+
+IRQ controller
+--------------
+An IRQ is generated when written to the interrupt raise register. The value
+appears in interrupt status register when the interrupt is raised and has to
+be written to the interrupt acknowledge register to lower it.
+
+DMA controller
+--------------
+One has to specify, source, destination, size, and start the transfer. One
+4096 bytes long buffer at offset 0x40000 is available in the EDU device. I.e.
+one can perform DMA to/from this space when programmed properly.
+
+Example of transferring a 100 byte block to and from the buffer using a given
+PCI address 'addr':
+addr     -> DMA source address
+0x40000  -> DMA destination address
+100      -> DMA transfer count
+1        -> DMA command register
+while (DMA command register & 1)
+       ;
+
+0x40000  -> DMA source address
+addr+100 -> DMA destination address
+100      -> DMA transfer count
+3        -> DMA command register
+while (DMA command register & 1)
+       ;
diff --git a/hw/misc/Makefile.objs b/hw/misc/Makefile.objs
index e47fea853065..029a56f279f1 100644
--- a/hw/misc/Makefile.objs
+++ b/hw/misc/Makefile.objs
@@ -40,3 +40,4 @@ obj-$(CONFIG_SLAVIO) += slavio_misc.o
 obj-$(CONFIG_ZYNQ) += zynq_slcr.o
 
 obj-$(CONFIG_PVPANIC) += pvpanic.o
+obj-$(CONFIG_EDU) += edu.o
diff --git a/hw/misc/edu.c b/hw/misc/edu.c
new file mode 100644
index 000000000000..c994a522bb33
--- /dev/null
+++ b/hw/misc/edu.c
@@ -0,0 +1,401 @@
+/*
+ * QEMU educational PCI device
+ *
+ * Copyright (c) 2012-2014 Jiri Slaby
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "hw/pci/pci.h"
+#include "qemu/timer.h"
+#include "qemu/main-loop.h" /* iothread mutex */
+#include "qapi/visitor.h"
+
+#define EDU(obj)        OBJECT_CHECK(EduState, obj, "edu")
+
+#define FACT_IRQ        0x00000001
+#define DMA_IRQ         0x00000100
+
+#define DMA_START       0x40000
+#define DMA_SIZE        4096
+
+typedef struct {
+    PCIDevice pdev;
+    MemoryRegion mmio;
+
+    QemuThread thread;
+    QemuMutex thr_mutex;
+    QemuCond thr_cond;
+    bool stopping;
+
+    uint32_t addr4;
+    uint32_t fact;
+#define EDU_STATUS_COMPUTING    0x01
+#define EDU_STATUS_IRQFACT      0x80
+    uint32_t status;
+
+    uint32_t irq_status;
+
+#define EDU_DMA_RUN             0x1
+#define EDU_DMA_DIR(cmd)        (((cmd) & 0x2) >> 1)
+# define EDU_DMA_FROM_PCI       0
+# define EDU_DMA_TO_PCI         1
+#define EDU_DMA_IRQ             0x4
+    struct dma_state {
+        dma_addr_t src;
+        dma_addr_t dst;
+        dma_addr_t cnt;
+        dma_addr_t cmd;
+    } dma;
+    QEMUTimer dma_timer;
+    char dma_buf[DMA_SIZE];
+    uint64_t dma_mask;
+} EduState;
+
+static void edu_raise_irq(EduState *edu, uint32_t val)
+{
+    edu->irq_status |= val;
+    if (edu->irq_status) {
+        pci_set_irq(&edu->pdev, 1);
+    }
+}
+
+static void edu_lower_irq(EduState *edu, uint32_t val)
+{
+    edu->irq_status &= ~val;
+
+    if (!edu->irq_status) {
+        pci_set_irq(&edu->pdev, 0);
+    }
+}
+
+static bool within(uint32_t addr, uint32_t start, uint32_t end)
+{
+    return start <= addr && addr < end;
+}
+
+static void edu_check_range(uint32_t addr, uint32_t size1, uint32_t start,
+                uint32_t size2)
+{
+    uint32_t end1 = addr + size1;
+    uint32_t end2 = start + size2;
+
+    if (within(addr, start, end2) &&
+            end1 > addr && within(end1, start, end2)) {
+        return;
+    }
+
+    hw_error("EDU: DMA range 0x%.8x-0x%.8x out of bounds (0x%.8x-0x%.8x)!",
+            addr, end1 - 1, start, end2 - 1);
+}
+
+static dma_addr_t edu_clamp_addr(const EduState *edu, dma_addr_t addr)
+{
+    dma_addr_t res = addr & edu->dma_mask;
+
+    if (addr != res) {
+        printf("EDU: clamping DMA 0x%.16lx to 0x%.16lx!\n", addr, res);
+    }
+
+    return res;
+}
+
+static void edu_dma_timer(void *opaque)
+{
+    EduState *edu = opaque;
+    bool raise_irq = false;
+
+    if (!(edu->dma.cmd & EDU_DMA_RUN)) {
+        return;
+    }
+
+    if (EDU_DMA_DIR(edu->dma.cmd) == EDU_DMA_FROM_PCI) {
+        uint32_t dst = edu->dma.dst;
+        edu_check_range(dst, edu->dma.cnt, DMA_START, DMA_SIZE);
+        dst -= DMA_START;
+        pci_dma_read(&edu->pdev, edu_clamp_addr(edu, edu->dma.src),
+                edu->dma_buf + dst, edu->dma.cnt);
+    } else {
+        uint32_t src = edu->dma.src;
+        edu_check_range(src, edu->dma.cnt, DMA_START, DMA_SIZE);
+        src -= DMA_START;
+        pci_dma_write(&edu->pdev, edu_clamp_addr(edu, edu->dma.dst),
+                edu->dma_buf + src, edu->dma.cnt);
+    }
+
+    edu->dma.cmd &= ~EDU_DMA_RUN;
+    if (edu->dma.cmd & EDU_DMA_IRQ) {
+        raise_irq = true;
+    }
+
+    if (raise_irq) {
+        edu_raise_irq(edu, DMA_IRQ);
+    }
+}
+
+static void dma_rw(EduState *edu, bool write, dma_addr_t *val, dma_addr_t *dma,
+                bool timer)
+{
+    if (write && (edu->dma.cmd & EDU_DMA_RUN)) {
+        return;
+    }
+
+    if (write) {
+        *dma = *val;
+    } else {
+        *val = *dma;
+    }
+
+    if (timer) {
+        timer_mod(&edu->dma_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 
100);
+    }
+}
+
+static uint64_t edu_mmio_read(void *opaque, hwaddr addr, unsigned size)
+{
+    EduState *edu = opaque;
+    uint64_t val = ~0ULL;
+
+    if (size != 4) {
+        return val;
+    }
+
+    switch (addr) {
+    case 0x00:
+        val = 0x010000edu;
+        break;
+    case 0x04:
+        val = edu->addr4;
+        break;
+    case 0x08:
+        qemu_mutex_lock(&edu->thr_mutex);
+        val = edu->fact;
+        qemu_mutex_unlock(&edu->thr_mutex);
+        break;
+    case 0x20:
+        val = atomic_read(&edu->status);
+        break;
+    case 0x24:
+        val = edu->irq_status;
+        break;
+    case 0x80:
+        dma_rw(edu, false, &val, &edu->dma.src, false);
+        break;
+    case 0x88:
+        dma_rw(edu, false, &val, &edu->dma.dst, false);
+        break;
+    case 0x90:
+        dma_rw(edu, false, &val, &edu->dma.cnt, false);
+        break;
+    case 0x98:
+        dma_rw(edu, false, &val, &edu->dma.cmd, false);
+        break;
+    }
+
+    return val;
+}
+
+static void edu_mmio_write(void *opaque, hwaddr addr, uint64_t val,
+                unsigned size)
+{
+    EduState *edu = opaque;
+
+    if (addr < 0x80 && size != 4) {
+        return;
+    }
+
+    if (addr >= 0x80 && size != 4 && size != 8) {
+        return;
+    }
+
+    switch (addr) {
+    case 0x04:
+        edu->addr4 = ~val;
+        break;
+    case 0x08:
+        if (atomic_fetch_or(&edu->status, EDU_STATUS_COMPUTING) & 
EDU_STATUS_COMPUTING) {
+            break;
+        }
+        qemu_mutex_lock(&edu->thr_mutex);
+        edu->fact = val;
+        qemu_cond_signal(&edu->thr_cond);
+        qemu_mutex_unlock(&edu->thr_mutex);
+        break;
+    case 0x20:
+        if (val & EDU_STATUS_IRQFACT) {
+            atomic_or(&edu->status, EDU_STATUS_IRQFACT);
+        } else {
+            atomic_and(&edu->status, ~EDU_STATUS_IRQFACT);
+        }
+        break;
+    case 0x60:
+        edu_raise_irq(edu, val);
+        break;
+    case 0x64:
+        edu_lower_irq(edu, val);
+        break;
+    case 0x80:
+        dma_rw(edu, true, &val, &edu->dma.src, false);
+        break;
+    case 0x88:
+        dma_rw(edu, true, &val, &edu->dma.dst, false);
+        break;
+    case 0x90:
+        dma_rw(edu, true, &val, &edu->dma.cnt, false);
+        break;
+    case 0x98:
+        if (!(val & EDU_DMA_RUN)) {
+            break;
+        }
+        dma_rw(edu, true, &val, &edu->dma.cmd, true);
+        break;
+    }
+}
+
+static const MemoryRegionOps edu_mmio_ops = {
+    .read = edu_mmio_read,
+    .write = edu_mmio_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+};
+
+/*
+ * We purposedly use a thread, so that users are forced to wait for the status
+ * register.
+ */
+static void *edu_fact_thread(void *opaque)
+{
+    EduState *edu = opaque;
+
+    while (1) {
+        uint32_t val, ret = 1;
+
+        qemu_mutex_lock(&edu->thr_mutex);
+        while ((atomic_read(&edu->status) & EDU_STATUS_COMPUTING) == 0 && 
!edu->stopping) {
+            qemu_cond_wait(&edu->thr_cond, &edu->thr_mutex);
+        }
+
+        if (edu->stopping) {
+            qemu_mutex_unlock(&edu->thr_mutex);
+            break;
+        }
+
+        val = edu->fact;
+        qemu_mutex_unlock(&edu->thr_mutex);
+
+        while (val > 0) {
+            ret *= val--;
+        }
+
+       /* we should sleep randomly here, so that students check the status 
properly */
+
+        qemu_mutex_lock(&edu->thr_mutex);
+        edu->fact = ret;
+        qemu_mutex_unlock(&edu->thr_mutex);
+        atomic_and(&edu->status, ~EDU_STATUS_COMPUTING);
+
+        if (atomic_read(&edu->status) & EDU_STATUS_IRQFACT) {
+            qemu_mutex_lock_iothread();
+            edu_raise_irq(edu, FACT_IRQ);
+            qemu_mutex_unlock_iothread();
+        }
+    }
+
+    return NULL;
+}
+
+static int pci_edu_init(PCIDevice *pdev)
+{
+    EduState *edu = DO_UPCAST(EduState, pdev, pdev);
+    uint8_t *pci_conf = pdev->config;
+
+    timer_init(&edu->dma_timer, main_loop_tlg.tl[QEMU_CLOCK_VIRTUAL], SCALE_MS,
+            edu_dma_timer, edu);
+
+    qemu_mutex_init(&edu->thr_mutex);
+    qemu_cond_init(&edu->thr_cond);
+    qemu_thread_create(&edu->thread, "edu", edu_fact_thread,
+                       edu, QEMU_THREAD_JOINABLE);
+
+    pci_config_set_interrupt_pin(pci_conf, 1);
+
+    memory_region_init_io(&edu->mmio, OBJECT(edu), &edu_mmio_ops, edu,
+                    "edu-mmio", 1 << 20);
+    pci_register_bar(pdev, 0, PCI_BASE_ADDRESS_SPACE_MEMORY, &edu->mmio);
+
+    return 0;
+}
+
+static void pci_edu_uninit(PCIDevice *pdev)
+{
+    EduState *edu = DO_UPCAST(EduState, pdev, pdev);
+
+    qemu_mutex_lock(&edu->thr_mutex);
+    edu->stopping = true;
+    qemu_mutex_unlock(&edu->thr_mutex);
+    qemu_cond_signal(&edu->thr_cond);
+    qemu_thread_join(&edu->thread);
+
+    qemu_cond_destroy(&edu->thr_cond);
+    qemu_mutex_destroy(&edu->thr_mutex);
+
+    timer_del(&edu->dma_timer);
+}
+
+static void edu_obj_uint64(Object *obj, struct Visitor *v, void *opaque,
+                const char *name, Error **errp)
+{
+    uint64_t *val = opaque;
+
+    visit_type_uint64(v, val, name, errp);
+}
+
+static void edu_instance_init(Object *obj)
+{
+    EduState *edu = EDU(obj);
+
+    edu->dma_mask = (1UL << 28) - 1;
+    object_property_add(obj, "dma_mask", "uint64", edu_obj_uint64,
+                    edu_obj_uint64, NULL, &edu->dma_mask, NULL);
+}
+
+static void edu_class_init(ObjectClass *class, void *data)
+{
+    PCIDeviceClass *k = PCI_DEVICE_CLASS(class);
+
+    k->init = pci_edu_init;
+    k->exit = pci_edu_uninit;
+    k->vendor_id = PCI_VENDOR_ID_QEMU;
+    k->device_id = 0x11e8;
+    k->revision = 0x10;
+    k->class_id = PCI_CLASS_OTHERS;
+}
+
+static void pci_edu_register_types(void)
+{
+    static const TypeInfo edu_info = {
+        .name          = "edu",
+        .parent        = TYPE_PCI_DEVICE,
+        .instance_size = sizeof(EduState),
+        .instance_init = edu_instance_init,
+        .class_init    = edu_class_init,
+    };
+
+    type_register_static(&edu_info);
+}
+type_init(pci_edu_register_types)
-- 
2.2.1