[SeaBIOS] [PATCH v2 1/2] QEMU DMA: Add DMA write capability

From: Ben Warren

This allows BIOS to write data back to QEMU using the DMA interface and
provides a higher-level abstraction to write to a fw_cfg file

Signed-off-by: Ben Warren 
---
 src/fw/paravirt.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/fw/paravirt.h |  3 +++
 2 files changed, 52 insertions(+)

diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
index 6de70f6..66404c7 100644
--- a/src/fw/paravirt.c
+++ b/src/fw/paravirt.c
@@ -253,6 +253,20 @@ qemu_cfg_read(void *buf, int len)
 }

static void
+qemu_cfg_write(void *buf, int len)
+{
+    if (len == 0) {
+        return;
+    }
+
+    if (qemu_cfg_dma_enabled()) {
+        qemu_cfg_dma_transfer(buf, len, QEMU_CFG_DMA_CTL_WRITE);
+    } else {
+        warn_internalerror();
+    }
+}
+
+static void
 qemu_cfg_skip(int len)
 {
     if (len == 0) {
@@ -280,6 +294,18 @@ qemu_cfg_read_entry(void *buf, int e, int len)
     }
 }

+static void
+qemu_cfg_write_entry(void *buf, int e, int len)
+{
+    if (qemu_cfg_dma_enabled()) {
+        u32 control = (e << 16) | QEMU_CFG_DMA_CTL_SELECT
+                        | QEMU_CFG_DMA_CTL_WRITE;
+        qemu_cfg_dma_transfer(buf, len, control);
+    } else {
+        warn_internalerror();
+    }
+}
+
 struct qemu_romfile_s {
     struct romfile_s file;
     int select, skip;
@@ -303,6 +329,29 @@ qemu_cfg_read_file(struct romfile_s *file, void *dst, u32 maxlen)
     return file->size;
 }

+int
+qemu_cfg_write_file(void *src, struct romfile_s *file, u32 maxlen)
+{
+    if (file->size < maxlen)
+        return -1;
+
+    if (!qemu_cfg_dma_enabled() || (file->copy != qemu_cfg_read_file)) {
+        warn_internalerror();
+        return -1;
+    }
+    struct qemu_romfile_s *qfile;
+    qfile = container_of(file, struct qemu_romfile_s, file);
+    if (qfile->skip == 0) {
+        /* Do it in one transfer */
+        qemu_cfg_write_entry(src, qfile->select, file->size);
+    } else {
+        qemu_cfg_select(qfile->select);
+        qemu_cfg_skip(qfile->skip);
+        qemu_cfg_write(src, file->size);
+    }
+    return file->size;
+}
+
 static void
 qemu_romfile_add(char *name, int select, int skip, int size)
 {
diff --git a/src/fw/paravirt.h b/src/fw/paravirt.h
index d8eb7c4..f88449a 100644
--- a/src/fw/paravirt.h
+++ b/src/fw/paravirt.h
@@ -3,6 +3,7 @@

#include "config.h" // CONFIG_*
 #include "biosvar.h" // GET_GLOBAL
+#include "romfile.h" // struct romfile_s

// Types of paravirtualized platforms.
 #define PF_QEMU     (1<<0)
@@ -43,6 +44,7 @@ static inline int runningOnKVM(void) {
 #define QEMU_CFG_DMA_CTL_READ    0x02
 #define QEMU_CFG_DMA_CTL_SKIP    0x04
 #define QEMU_CFG_DMA_CTL_SELECT  0x08
+#define QEMU_CFG_DMA_CTL_WRITE   0x10

// QEMU_CFG_DMA ID bit
 #define QEMU_CFG_VERSION_DMA    2
@@ -53,5 +55,6 @@ void qemu_platform_setup(void);
 void qemu_cfg_init(void);

u16 qemu_get_present_cpus_count(void);
+int qemu_cfg_write_file(void *src, struct romfile_s *file, u32 maxlen);

#endif