[PATCH v14 9/9] RFC: fw_cfg: do DMA read operation
From: Marc-Andrà Lureau
Date: Wed Feb 14 2018 - 09:20:06 EST
Modify fw_cfg_read_blob() to use DMA if the device supports it.
Return errors, because the operation may fail.
So far, only one call in fw_cfg_register_dir_entries() is using
kmalloc'ed buf and is thus clearly eligible to DMA read.
Initially, I didn't implement DMA read to speed up boot time, but as a
first step before introducing DMA write (since read operations were
already presents). Even more, I didn't realize fw-cfg entries were
being read by the kernel during boot by default. But actally fw-cfg
entries are being populated during module probe. I knew DMA improved a
lot bios boot time (the main reason the DMA interface was added
afaik). Let see the time it would take to read the whole ACPI
tables (128kb allocated)
# time cat /sys/firmware/qemu_fw_cfg/by_name/etc/acpi/tables/raw
- with DMA: sys 0m0.003s
- without DMA (-global fw_cfg.dma_enabled=off): sys 0m7.674s
FW_CFG_FILE_DIR (0x19) is the only "file" that is read during kernel
boot to populate sysfs qemu_fw_cfg directory, and it is quite
small (1-2kb). Since it does not expose itself, in order to measure
the time it takes to read such small file, I took a comparable sized
file of 2048 bytes and exposed it (-fw_cfg test,file=file with a
modified read_raw enabling DMA)
# perf stat -r 100 cat /sys/firmware/qemu_fw_cfg/by_name/test/raw >/dev/null
- with DMA:
0.636037 task-clock (msec) # 0.141 CPUs utilized ( +- 1.19% )
- without DMA:
6.430128 task-clock (msec) # 0.622 CPUs utilized ( +- 0.22% )
That's a few msec saved during boot by enabling DMA read (the gain
would be more substantial if other & bigger fw-cfg entries are read by
others from sysfs, unfortunately, it's not clear if we can always
enable DMA there)
Signed-off-by: Marc-Andrà Lureau <marcandre.lureau@xxxxxxxxxx>
---
drivers/firmware/qemu_fw_cfg.c | 80 ++++++++++++++++++++++++++++++++++--------
1 file changed, 66 insertions(+), 14 deletions(-)
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 69939e2529f2..ba9b907a4399 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -124,12 +124,46 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
return ret;
}
+/* with acpi & dev locks taken */
+static ssize_t fw_cfg_read_blob_dma(u16 key,
+ void *buf, loff_t pos, size_t count)
+{
+ ssize_t ret;
+
+ if (pos == 0) {
+ ret = fw_cfg_dma_transfer(buf, count, key << 16
+ | FW_CFG_DMA_CTL_SELECT
+ | FW_CFG_DMA_CTL_READ);
+ } else {
+ iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
+ ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP);
+ if (ret < 0)
+ return ret;
+ ret = fw_cfg_dma_transfer(buf, count,
+ FW_CFG_DMA_CTL_READ);
+ }
+
+ return ret;
+}
+
+/* with acpi & dev locks taken */
+static void fw_cfg_read_blob_io(u16 key,
+ void *buf, loff_t pos, size_t count)
+{
+ iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
+ while (pos-- > 0)
+ ioread8(fw_cfg_reg_data);
+ ioread8_rep(fw_cfg_reg_data, buf, count);
+}
+
/* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
-static inline void fw_cfg_read_blob(u16 key,
- void *buf, loff_t pos, size_t count)
+static ssize_t fw_cfg_read_blob(u16 key,
+ void *buf, loff_t pos, size_t count,
+ bool dma)
{
u32 glk = -1U;
acpi_status status;
+ ssize_t ret = count;
/* If we have ACPI, ensure mutual exclusion against any potential
* device access by the firmware, e.g. via AML methods:
@@ -139,17 +173,21 @@ static inline void fw_cfg_read_blob(u16 key,
/* Should never get here */
WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n");
memset(buf, 0, count);
- return;
+ return -EINVAL;
}
mutex_lock(&fw_cfg_dev_lock);
- iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
- while (pos-- > 0)
- ioread8(fw_cfg_reg_data);
- ioread8_rep(fw_cfg_reg_data, buf, count);
+ if (dma && fw_cfg_dma_enabled()) {
+ ret = fw_cfg_read_blob_dma(key, buf, pos, count);
+ } else {
+ fw_cfg_read_blob_io(key, buf, pos, count);
+ }
+
mutex_unlock(&fw_cfg_dev_lock);
acpi_release_global_lock(glk);
+
+ return ret;
}
#ifdef CONFIG_CRASH_CORE
@@ -282,8 +320,9 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
#endif
/* verify fw_cfg device signature */
- fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
- if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
+ if (fw_cfg_read_blob(FW_CFG_SIGNATURE, sig,
+ 0, FW_CFG_SIG_SIZE, false) < 0 ||
+ memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
fw_cfg_io_cleanup();
return -ENODEV;
}
@@ -466,8 +505,8 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
if (count > entry->size - pos)
count = entry->size - pos;
- fw_cfg_read_blob(entry->select, buf, pos, count);
- return count;
+ /* do not use DMA, virt_to_phys(buf) might not be ok */
+ return fw_cfg_read_blob(entry->select, buf, pos, count, false);
}
static struct bin_attribute fw_cfg_sysfs_attr_raw = {
@@ -632,7 +671,12 @@ static int fw_cfg_register_dir_entries(void)
struct fw_cfg_file *dir;
size_t dir_size;
- fw_cfg_read_blob(FW_CFG_FILE_DIR, &files.count, 0, sizeof(files.count));
+ ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, &files.count,
+ 0, sizeof(files.count), false);
+ if (ret < 0) {
+ return ret;
+ }
+
count = be32_to_cpu(files.count);
dir_size = count * sizeof(struct fw_cfg_file);
@@ -640,7 +684,11 @@ static int fw_cfg_register_dir_entries(void)
if (!dir)
return -ENOMEM;
- fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(files.count), dir_size);
+ ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, dir,
+ sizeof(files.count), dir_size, false);
+ if (ret < 0) {
+ goto end;
+ }
for (i = 0; i < count; i++) {
ret = fw_cfg_register_file(&dir[i]);
@@ -648,6 +696,7 @@ static int fw_cfg_register_dir_entries(void)
break;
}
+end:
kfree(dir);
return ret;
}
@@ -688,7 +737,10 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev)
goto err_probe;
/* get revision number, add matching top-level attribute */
- fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev));
+ err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev), false);
+ if (err < 0) {
+ goto err_probe;
+ }
fw_cfg_rev = le32_to_cpu(rev);
err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
if (err)
--
2.16.1.73.g5832b7e9f2