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-André Lureau <marcandre.lur...@redhat.com> --- drivers/firmware/qemu_fw_cfg.c | 47 ++++++++++++++++++++++++++++++------------ 1 file changed, 34 insertions(+), 13 deletions(-) diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c index fd576ba7b337..3721dc868a2b 100644 --- a/drivers/firmware/qemu_fw_cfg.c +++ b/drivers/firmware/qemu_fw_cfg.c @@ -150,11 +150,13 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control) } /* 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: @@ -164,17 +166,36 @@ 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()) { + 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) + goto end; + ret = fw_cfg_dma_transfer(buf, count, + FW_CFG_DMA_CTL_READ); + } + } else { + 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); + } + +end: mutex_unlock(&fw_cfg_dev_lock); acpi_release_global_lock(glk); + + return ret; } #ifdef CONFIG_CRASH_CORE @@ -307,7 +328,7 @@ 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); + fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE, false); if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) { fw_cfg_io_cleanup(); return -ENODEV; @@ -494,8 +515,8 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj, if (count > entry->f.size - pos) count = entry->f.size - pos; - fw_cfg_read_blob(entry->f.select, buf, pos, count); - return count; + /* do not use DMA, virt_to_phys(buf) might not be ok */ + return fw_cfg_read_blob(entry->f.select, buf, pos, count, false); } static struct bin_attribute fw_cfg_sysfs_attr_raw = { @@ -656,7 +677,7 @@ 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, &count, 0, sizeof(count)); + fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count), false); count = be32_to_cpu(count); dir_size = count * sizeof(struct fw_cfg_file); @@ -664,7 +685,7 @@ static int fw_cfg_register_dir_entries(void) if (!dir) return -ENOMEM; - fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size); + fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size, true); for (i = 0; i < count; i++) { dir[i].size = be32_to_cpu(dir[i].size); @@ -713,7 +734,7 @@ 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, &fw_cfg_rev, 0, sizeof(fw_cfg_rev)); + fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev), false); fw_cfg_rev = le32_to_cpu(fw_cfg_rev); err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr); if (err) -- 2.16.1.73.g5832b7e9f2