3 files changed, 185 insertions, 1 deletions

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index d9aa43d78bcc..25fb8bcf32a2 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -704,12 +704,24 @@ this directory the following files can currently be found:
                                 The current number of free dma_debug_entries
                                 in the allocator.
 
+        dma-api/driver-filter
+                                You can write a name of a driver into this file
+                                to limit the debug output to requests from that
+                                particular driver. Write an empty string to
+                                that file to disable the filter and see
+                                all errors again.
+
 If you have this code compiled into your kernel it will be enabled by default.
 If you want to boot without the bookkeeping anyway you can provide
 'dma_debug=off' as a boot parameter. This will disable DMA-API debugging.
 Notice that you can not enable it again at runtime. You have to reboot to do
 so.
 
+If you want to see debug messages only for a special device driver you can
+specify the dma_debug_driver=<drivername> parameter. This will enable the
+driver filter at boot time. The debug code will only print errors for that
+driver afterwards. This filter can be disabled or changed later using debugfs.
+
 When the code disables itself at runtime this is most likely because it ran
 out of dma_debug_entries. These entries are preallocated at boot. The number
 of preallocated entries is defined per architecture. If it is too low for you
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e87bdbfbcc75..b3f1314588c9 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -646,6 +646,13 @@ and is between 256 and 4096 characters. It is defined in the file
                         DMA-API debugging code disables itself because the
                         architectural default is too low.
 
+        dma_debug_driver=<driver_name>
+                        With this option the DMA-API debugging driver
+                        filter feature can be enabled at boot time. Just
+                        pass the driver to filter for as the parameter.
+                        The filter can be disabled or changed to another
+                        driver later using sysfs.
+
         dscc4.setup=    [NET]
 
         dtc3181e=       [HW,SCSI]
diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 1abed176d35a..f49ab22643b7 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -23,9 +23,11 @@
 #include <linux/dma-debug.h>
 #include <linux/spinlock.h>
 #include <linux/debugfs.h>
+#include <linux/uaccess.h>
 #include <linux/device.h>
 #include <linux/types.h>
 #include <linux/sched.h>
+#include <linux/ctype.h>
 #include <linux/list.h>
 #include <linux/slab.h>
 
@@ -98,6 +100,16 @@ static struct dentry *show_all_errors_dent  __read_mostly;
 static struct dentry *show_num_errors_dent  __read_mostly;
 static struct dentry *num_free_entries_dent __read_mostly;
 static struct dentry *min_free_entries_dent __read_mostly;
+static struct dentry *filter_dent           __read_mostly;
+
+/* per-driver filter related state */
+
+#define NAME_MAX_LEN    64
+
+static char                  current_driver_name[NAME_MAX_LEN] __read_mostly;
+static struct device_driver *current_driver                    __read_mostly;
+
+static DEFINE_RWLOCK(driver_name_lock);
 
 static const char *type2name[4] = { "single", "page",
                                     "scather-gather", "coherent" };
@@ -133,9 +145,48 @@ static inline void dump_entry_trace(struct dma_debug_entry *entry)
 #endif
 }
 
+static bool driver_filter(struct device *dev)
+{
+        /* driver filter off */
+        if (likely(!current_driver_name[0]))
+                return true;
+
+        /* driver filter on and initialized */
+        if (current_driver && dev->driver == current_driver)
+                return true;
+
+        /* driver filter on but not yet initialized */
+        if (!current_driver && current_driver_name[0]) {
+                struct device_driver *drv = get_driver(dev->driver);
+                unsigned long flags;
+                bool ret = false;
+
+                if (!drv)
+                        return false;
+
+                /* lock to protect against change of current_driver_name */
+                read_lock_irqsave(&driver_name_lock, flags);
+
+                if (drv->name &&
+                    strncmp(current_driver_name, drv->name,
+                            NAME_MAX_LEN-1) == 0) {
+                        current_driver = drv;
+                        ret = true;
+                }
+
+                read_unlock_irqrestore(&driver_name_lock, flags);
+                put_driver(drv);
+
+                return ret;
+        }
+
+        return false;
+}
+
 #define err_printk(dev, entry, format, arg...) do {             \
                 error_count += 1;                               \
-                if (show_all_errors || show_num_errors > 0) {   \
+                if (driver_filter(dev) &&                       \
+                    (show_all_errors || show_num_errors > 0)) { \
                         WARN(1, "%s %s: " format,               \
                              dev_driver_string(dev),            \
                              dev_name(dev) , ## arg);           \
@@ -412,6 +463,97 @@ out_err:
         return -ENOMEM;
 }
 
+static ssize_t filter_read(struct file *file, char __user *user_buf,
+                           size_t count, loff_t *ppos)
+{
+        unsigned long flags;
+        char buf[NAME_MAX_LEN + 1];
+        int len;
+
+        if (!current_driver_name[0])
+                return 0;
+
+        /*
+         * We can't copy to userspace directly because current_driver_name can
+         * only be read under the driver_name_lock with irqs disabled. So
+         * create a temporary copy first.
+         */
+        read_lock_irqsave(&driver_name_lock, flags);
+        len = scnprintf(buf, NAME_MAX_LEN + 1, "%s\n", current_driver_name);
+        read_unlock_irqrestore(&driver_name_lock, flags);
+
+        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+}
+
+static ssize_t filter_write(struct file *file, const char __user *userbuf,
+                            size_t count, loff_t *ppos)
+{
+        unsigned long flags;
+        char buf[NAME_MAX_LEN];
+        size_t len = NAME_MAX_LEN - 1;
+        int i;
+
+        /*
+         * We can't copy from userspace directly. Access to
+         * current_driver_name is protected with a write_lock with irqs
+         * disabled. Since copy_from_user can fault and may sleep we
+         * need to copy to temporary buffer first
+         */
+        len = min(count, len);
+        if (copy_from_user(buf, userbuf, len))
+                return -EFAULT;
+
+        buf[len] = 0;
+
+        write_lock_irqsave(&driver_name_lock, flags);
+
+        /* Now handle the string we got from userspace very carefully.
+         * The rules are:
+         *         - only use the first token we got
+         *         - token delimiter is everything looking like a space
+         *           character (' ', '\n', '\t' ...)
+         *
+         */
+        if (!isalnum(buf[0])) {
+                /*
+                   If the first character userspace gave us is not
+                 * alphanumerical then assume the filter should be
+                 * switched off.
+                 */
+                if (current_driver_name[0])
+                        printk(KERN_INFO "DMA-API: switching off dma-debug "
+                                         "driver filter\n");
+                current_driver_name[0] = 0;
+                current_driver = NULL;
+                goto out_unlock;
+        }
+
+        /*
+         * Now parse out the first token and use it as the name for the
+         * driver to filter for.
+         */
+        for (i = 0; i < NAME_MAX_LEN; ++i) {
+                current_driver_name[i] = buf[i];
+                if (isspace(buf[i]) || buf[i] == ' ' || buf[i] == 0)
+                        break;
+        }
+        current_driver_name[i] = 0;
+        current_driver = NULL;
+
+        printk(KERN_INFO "DMA-API: enable driver filter for driver [%s]\n",
+               current_driver_name);
+
+out_unlock:
+        write_unlock_irqrestore(&driver_name_lock, flags);
+
+        return count;
+}
+
+const struct file_operations filter_fops = {
+        .read  = filter_read,
+        .write = filter_write,
+};
+
 static int dma_debug_fs_init(void)
 {
         dma_debug_dent = debugfs_create_dir("dma-api", NULL);
@@ -455,6 +597,11 @@ static int dma_debug_fs_init(void)
         if (!min_free_entries_dent)
                 goto out_err;
 
+        filter_dent = debugfs_create_file("driver_filter", 0644,
+                                          dma_debug_dent, NULL, &filter_fops);
+        if (!filter_dent)
+                goto out_err;
+
         return 0;
 
 out_err:
@@ -1044,3 +1191,21 @@ void debug_dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
 }
 EXPORT_SYMBOL(debug_dma_sync_sg_for_device);
 
+static int __init dma_debug_driver_setup(char *str)
+{
+        int i;
+
+        for (i = 0; i < NAME_MAX_LEN - 1; ++i, ++str) {
+                current_driver_name[i] = *str;
+                if (*str == 0)
+                        break;
+        }
+
+        if (current_driver_name[0])
+                printk(KERN_INFO "DMA-API: enable driver filter for "
+                                 "driver [%s]\n", current_driver_name);
+
+
+        return 1;
+}
+__setup("dma_debug_driver=", dma_debug_driver_setup);