[PATCH v4 19/23] xen/arm: Allow vpl011 to be used by DomU

[Stefano Stabellini <sstabellini@kernel.org>]

Make vpl011 being able to be used without a userspace component in Dom0.
In that case, output is printed to the Xen serial and input is received
from the Xen serial one character at a time.

Call domain_vpl011_init during construct_domU if vpl011 is enabled.

Introduce a new ring struct with only the ring array to avoid a waste of
memory. Introduce separate read_data and write_data functions for
initial domains: vpl011_write_data_xen is very simple and just writes
to the console, while vpl011_read_data_xen is a duplicate of
vpl011_read_data. Although textually almost identical, we are forced to
duplicate the functions because the struct layout is different.

Output characters are printed one by one, potentially leading to
intermixed output of different domains on the console. A follow-up patch
will solve the issue by introducing buffering.

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
---
Changes in v4:
- code style

Changes in v3:
- add in-code comments
- improve existing comments
- remove ifdef around domain_vpl011_init in construct_domU
- add ASSERT
- use SBSA_UART_FIFO_SIZE for in buffer size
- rename ring_enable to backend_in_domain
- rename struct xencons_in to struct vpl011_xen_backend
- rename inring field to xen
- rename helper functions accordingly
- remove unnecessary stub implementation of vpl011_rx_char
- move vpl011_rx_char_xen within the file to avoid the need of a forward
  declaration of vpl011_data_avail
- fix small bug in vpl011_rx_char_xen: increment in_prod before using it
  to check xencons_queued.

Changes in v2:
- only init if vpl011
- rename vpl011_read_char to vpl011_rx_char
- remove spurious change
- fix coding style
- use different ring struct
- move the write_data changes to their own function
  (vpl011_write_data_noring)
- duplicate vpl011_read_data
---
 xen/arch/arm/domain_build.c  |   9 +-
 xen/arch/arm/vpl011.c        | 200 +++++++++++++++++++++++++++++++++++++------
 xen/include/asm-arm/vpl011.h |   8 ++
 3 files changed, 192 insertions(+), 25 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 049ab84..4379538 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2618,7 +2618,14 @@ static int __init construct_domU(struct domain *d,
     if ( rc < 0 )
         return rc;
 
-    return __construct_domain(d, &kinfo);
+    rc = __construct_domain(d, &kinfo);
+    if ( rc < 0 )
+        return rc;
+
+    if ( kinfo.vpl011 )
+        rc = domain_vpl011_init(d, NULL);
+
+    return rc;
 }
 
 void __init create_domUs(void)
diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index 68452a8..131507e 100644
--- a/xen/arch/arm/vpl011.c
+++ b/xen/arch/arm/vpl011.c
@@ -77,6 +77,91 @@ static void vpl011_update_interrupt_status(struct domain *d)
 #endif
 }
 
+/*
+ * vpl011_write_data_xen writes chars from the vpl011 out buffer to the
+ * console. Only to be used when the backend is Xen.
+ */
+static void vpl011_write_data_xen(struct domain *d, uint8_t data)
+{
+    unsigned long flags;
+    struct vpl011 *vpl011 = &d->arch.vpl011;
+
+    VPL011_LOCK(d, flags);
+
+    printk("%c", data);
+    if (data == '\n')
+        printk("DOM%u: ", d->domain_id);
+
+    vpl011->uartris |= TXI;
+    vpl011->uartfr &= ~TXFE;
+    vpl011_update_interrupt_status(d);
+
+    VPL011_UNLOCK(d, flags);
+}
+
+/*
+ * vpl011_read_data_xen reads data when the backend is xen. Characters
+ * are added to the vpl011 receive buffer by vpl011_rx_char_xen.
+ */
+static uint8_t vpl011_read_data_xen(struct domain *d)
+{
+    unsigned long flags;
+    uint8_t data = 0;
+    struct vpl011 *vpl011 = &d->arch.vpl011;
+    struct vpl011_xen_backend *intf = vpl011->backend.xen;
+    XENCONS_RING_IDX in_cons, in_prod;
+
+    VPL011_LOCK(d, flags);
+
+    in_cons = intf->in_cons;
+    in_prod = intf->in_prod;
+
+    smp_rmb();
+
+    /*
+     * It is expected that there will be data in the ring buffer when this
+     * function is called since the guest is expected to read the data register
+     * only if the TXFE flag is not set.
+     * If the guest still does read when TXFE bit is set then 0 will be returned.
+     */
+    if ( xencons_queued(in_prod, in_cons, sizeof(intf->in)) > 0 )
+    {
+        unsigned int fifo_level;
+
+        data = intf->in[xencons_mask(in_cons, sizeof(intf->in))];
+        in_cons += 1;
+        smp_mb();
+        intf->in_cons = in_cons;
+
+        fifo_level = xencons_queued(in_prod, in_cons, sizeof(intf->in));
+
+        /* If the FIFO is now empty, we clear the receive timeout interrupt. */
+        if ( fifo_level == 0 )
+        {
+            vpl011->uartfr |= RXFE;
+            vpl011->uartris &= ~RTI;
+        }
+
+        /* If the FIFO is more than half empty, we clear the RX interrupt. */
+        if ( fifo_level < sizeof(intf->in) - SBSA_UART_FIFO_LEVEL )
+            vpl011->uartris &= ~RXI;
+
+        vpl011_update_interrupt_status(d);
+    }
+    else
+        gprintk(XENLOG_ERR, "vpl011: Unexpected IN ring buffer empty\n");
+
+    /*
+     * We have consumed a character or the FIFO was empty, so clear the
+     * "FIFO full" bit.
+     */
+    vpl011->uartfr &= ~RXFF;
+
+    VPL011_UNLOCK(d, flags);
+
+    return data;
+}
+
 static uint8_t vpl011_read_data(struct domain *d)
 {
     unsigned long flags;
@@ -240,7 +325,10 @@ static int vpl011_mmio_read(struct vcpu *v,
     case DR:
         if ( !vpl011_reg32_check_access(dabt) ) goto bad_width;
 
-        *r = vreg_reg32_extract(vpl011_read_data(d), info);
+        if ( vpl011->backend_in_domain )
+            *r = vreg_reg32_extract(vpl011_read_data(d), info);
+        else
+            *r = vreg_reg32_extract(vpl011_read_data_xen(d), info);
         return 1;
 
     case RSR:
@@ -325,7 +413,10 @@ static int vpl011_mmio_write(struct vcpu *v,
 
         vreg_reg32_update(&data, r, info);
         data &= 0xFF;
-        vpl011_write_data(v->domain, data);
+        if ( vpl011->backend_in_domain )
+            vpl011_write_data(v->domain, data);
+        else
+            vpl011_write_data_xen(v->domain, data);
         return 1;
     }
 
@@ -430,6 +521,39 @@ static void vpl011_data_avail(struct domain *d,
         vpl011->uartfr |= TXFE;
 }
 
+/*
+ * vpl011_rx_char_xen adds a char to a domain's vpl011 receive buffer.
+ * It is only used when the vpl011 backend is in Xen.
+ */
+void vpl011_rx_char_xen(struct domain *d, char c)
+{
+    unsigned long flags;
+    struct vpl011 *vpl011 = &d->arch.vpl011;
+    struct vpl011_xen_backend *intf = vpl011->backend.xen;
+    XENCONS_RING_IDX in_cons, in_prod, in_fifo_level;
+
+    ASSERT(!vpl011->backend_in_domain);
+    VPL011_LOCK(d, flags);
+
+    in_cons = intf->in_cons;
+    in_prod = intf->in_prod;
+    if ( xencons_queued(in_prod, in_cons, sizeof(intf->in)) == sizeof(intf->in) )
+    {
+        VPL011_UNLOCK(d, flags);
+        return;
+    }
+
+    intf->in[xencons_mask(in_prod, sizeof(intf->in))] = c;
+    intf->in_prod = ++in_prod;
+
+    in_fifo_level = xencons_queued(in_prod,
+                                   in_cons,
+                                   sizeof(intf->in));
+
+    vpl011_data_avail(d, in_fifo_level, sizeof(intf->in), 0, SBSA_UART_FIFO_SIZE);
+    VPL011_UNLOCK(d, flags);
+}
+
 static void vpl011_notification(struct vcpu *v, unsigned int port)
 {
     unsigned long flags;
@@ -470,27 +594,47 @@ int domain_vpl011_init(struct domain *d, struct vpl011_init_info *info)
     if ( vpl011->backend.dom.ring_buf )
         return -EINVAL;
 
-    /* Map the guest PFN to Xen address space. */
-    rc =  prepare_ring_for_helper(d,
-                                  gfn_x(info->gfn),
-                                  &vpl011->backend.dom.ring_page,
-                                  &vpl011->backend.dom.ring_buf);
-    if ( rc < 0 )
-        goto out;
+    /*
+     * info is NULL when the backend is in Xen.
+     * info is != NULL when the backend is in a domain.
+     */
+    if ( info != NULL )
+    {
+        vpl011->backend_in_domain = true;
+
+        /* Map the guest PFN to Xen address space. */
+        rc =  prepare_ring_for_helper(d,
+                                      gfn_x(info->gfn),
+                                      &vpl011->backend.dom.ring_page,
+                                      &vpl011->backend.dom.ring_buf);
+        if ( rc < 0 )
+            goto out;
+
+        rc = alloc_unbound_xen_event_channel(d, 0, info->console_domid,
+                                             vpl011_notification);
+        if ( rc < 0 )
+            goto out1;
+
+        vpl011->evtchn = info->evtchn = rc;
+    }
+    else
+    {
+        vpl011->backend_in_domain = false;
+
+        vpl011->backend.xen = xzalloc(struct vpl011_xen_backend);
+        if ( vpl011->backend.xen == NULL )
+        {
+            rc = -EINVAL;
+            goto out1;
+        }
+    }
 
     rc = vgic_reserve_virq(d, GUEST_VPL011_SPI);
     if ( !rc )
     {
         rc = -EINVAL;
-        goto out1;
-    }
-
-    rc = alloc_unbound_xen_event_channel(d, 0, info->console_domid,
-                                         vpl011_notification);
-    if ( rc < 0 )
         goto out2;
-
-    vpl011->evtchn = info->evtchn = rc;
+    }
 
     spin_lock_init(&vpl011->lock);
 
@@ -503,8 +647,11 @@ out2:
     vgic_free_virq(d, GUEST_VPL011_SPI);
 
 out1:
-    destroy_ring_for_helper(&vpl011->backend.dom.ring_buf,
-			                vpl011->backend.dom.ring_page);
+    if ( vpl011->backend_in_domain )
+        destroy_ring_for_helper(&vpl011->backend.dom.ring_buf,
+                                vpl011->backend.dom.ring_page);
+    else
+        xfree(vpl011->backend.xen);
 
 out:
     return rc;
@@ -514,12 +661,17 @@ void domain_vpl011_deinit(struct domain *d)
 {
     struct vpl011 *vpl011 = &d->arch.vpl011;
 
-    if ( !vpl011->backend.dom.ring_buf )
-        return;
+    if ( vpl011->backend_in_domain )
+    {
+        if ( !vpl011->backend.dom.ring_buf )
+            return;
 
-    free_xen_event_channel(d, vpl011->evtchn);
-    destroy_ring_for_helper(&vpl011->backend.dom.ring_buf,
-			                vpl011->backend.dom.ring_page);
+        free_xen_event_channel(d, vpl011->evtchn);
+        destroy_ring_for_helper(&vpl011->backend.dom.ring_buf,
+                                vpl011->backend.dom.ring_page);
+    }
+    else
+        xfree(vpl011->backend.xen);
 }
 
 /*
diff --git a/xen/include/asm-arm/vpl011.h b/xen/include/asm-arm/vpl011.h
index 42d7a24..5eb6d25 100644
--- a/xen/include/asm-arm/vpl011.h
+++ b/xen/include/asm-arm/vpl011.h
@@ -21,6 +21,7 @@
 
 #include <public/domctl.h>
 #include <public/io/ring.h>
+#include <public/io/console.h>
 #include <asm/vreg.h>
 #include <xen/mm.h>
 
@@ -29,13 +30,19 @@
 #define VPL011_UNLOCK(d,flags) spin_unlock_irqrestore(&(d)->arch.vpl011.lock, flags)
 
 #define SBSA_UART_FIFO_SIZE 32
+struct vpl011_xen_backend {
+    char in[SBSA_UART_FIFO_SIZE];
+    XENCONS_RING_IDX in_cons, in_prod;
+};
 
 struct vpl011 {
+    bool backend_in_domain;
     union {
         struct {
             void *ring_buf;
             struct page_info *ring_page;
         } dom;
+        struct vpl011_xen_backend *xen;
     } backend;
     uint32_t    uartfr;         /* Flag register */
     uint32_t    uartcr;         /* Control register */
@@ -57,6 +64,7 @@ struct vpl011_init_info {
 int domain_vpl011_init(struct domain *d,
                        struct vpl011_init_info *info);
 void domain_vpl011_deinit(struct domain *d);
+void vpl011_rx_char_xen(struct domain *d, char c);
 #else
 static inline int domain_vpl011_init(struct domain *d,
                                      struct vpl011_init_info *info)
-- 
1.9.1


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