mmc: core: add random fault injection

This adds support to inject data errors after a completed host transfer.
The mmc core will return error even though the host transfer is successful.
This simple fault injection proved to be very useful to test the
non-blocking error handling in the mmc_blk_issue_rw_rq().
Random faults can also test how the host driver handles pre_req()
and post_req() in case of errors.

Signed-off-by: Per Forlin <per.forlin@linaro.org>
Acked-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

4 files changed, 82 insertions, 0 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index b27b94078c21..eb3069dfea8e 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -24,6 +24,8 @@
 #include <linux/regulator/consumer.h>
 #include <linux/pm_runtime.h>
 #include <linux/suspend.h>
+#include <linux/fault-inject.h>
+#include <linux/random.h>
 
 #include <linux/mmc/card.h>
 #include <linux/mmc/host.h>
@@ -83,6 +85,43 @@ static void mmc_flush_scheduled_work(void)
         flush_workqueue(workqueue);
 }
 
+#ifdef CONFIG_FAIL_MMC_REQUEST
+
+/*
+ * Internal function. Inject random data errors.
+ * If mmc_data is NULL no errors are injected.
+ */
+static void mmc_should_fail_request(struct mmc_host *host,
+                                    struct mmc_request *mrq)
+{
+        struct mmc_command *cmd = mrq->cmd;
+        struct mmc_data *data = mrq->data;
+        static const int data_errors[] = {
+                -ETIMEDOUT,
+                -EILSEQ,
+                -EIO,
+        };
+
+        if (!data)
+                return;
+
+        if (cmd->error || data->error ||
+            !should_fail(&host->fail_mmc_request, data->blksz * data->blocks))
+                return;
+
+        data->error = data_errors[random32() % ARRAY_SIZE(data_errors)];
+        data->bytes_xfered = (random32() % (data->bytes_xfered >> 9)) << 9;
+}
+
+#else /* CONFIG_FAIL_MMC_REQUEST */
+
+static inline void mmc_should_fail_request(struct mmc_host *host,
+                                           struct mmc_request *mrq)
+{
+}
+
+#endif /* CONFIG_FAIL_MMC_REQUEST */
+
 /**
  *      mmc_request_done - finish processing an MMC request
  *      @host: MMC host which completed request
@@ -109,6 +148,8 @@ void mmc_request_done(struct mmc_host *host, struct mmc_request *mrq)
                 cmd->error = 0;
                 host->ops->request(host, mrq);
         } else {
+                mmc_should_fail_request(host, mrq);
+
                 led_trigger_event(host->led, LED_OFF);
 
                 pr_debug("%s: req done (CMD%u): %d: %08x %08x %08x %08x\n",
diff --git a/drivers/mmc/core/debugfs.c b/drivers/mmc/core/debugfs.c
index 998797ed67a6..5acd707699c9 100644
--- a/drivers/mmc/core/debugfs.c
+++ b/drivers/mmc/core/debugfs.c
@@ -12,6 +12,7 @@
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/stat.h>
+#include <linux/fault-inject.h>
 
 #include <linux/mmc/card.h>
 #include <linux/mmc/host.h>
@@ -158,6 +159,23 @@ static int mmc_clock_opt_set(void *data, u64 val)
         return 0;
 }
 
+#ifdef CONFIG_FAIL_MMC_REQUEST
+
+static DECLARE_FAULT_ATTR(fail_mmc_request);
+
+#ifdef KERNEL
+/*
+ * Internal function. Pass the boot param fail_mmc_request to
+ * the setup fault injection attributes routine.
+ */
+static int __init setup_fail_mmc_request(char *str)
+{
+        return setup_fault_attr(&fail_mmc_request, str);
+}
+__setup("fail_mmc_request=", setup_fail_mmc_request);
+#endif /* KERNEL */
+#endif /* CONFIG_FAIL_MMC_REQUEST */
+
 DEFINE_SIMPLE_ATTRIBUTE(mmc_clock_fops, mmc_clock_opt_get, mmc_clock_opt_set,
         "%llu\n");
 
@@ -188,6 +206,13 @@ void mmc_add_host_debugfs(struct mmc_host *host)
                                 root, &host->clk_delay))
                 goto err_node;
 #endif
+#ifdef CONFIG_FAIL_MMC_REQUEST
+        host->fail_mmc_request = fail_mmc_request;
+        if (IS_ERR(fault_create_debugfs_attr("fail_mmc_request",
+                                             root,
+                                             &host->fail_mmc_request)))
+                goto err_node;
+#endif
         return;
 
 err_node:
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 1d09562ccf73..4c4bddf5ef61 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -12,6 +12,7 @@
 
 #include <linux/leds.h>
 #include <linux/sched.h>
+#include <linux/fault-inject.h>
 
 #include <linux/mmc/core.h>
 #include <linux/mmc/pm.h>
@@ -302,6 +303,10 @@ struct mmc_host {
 
         struct mmc_async_req    *areq;          /* active async req */
 
+#ifdef CONFIG_FAIL_MMC_REQUEST
+        struct fault_attr       fail_mmc_request;
+#endif
+
         unsigned long           private[0] ____cacheline_aligned;
 };
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c0cb9c4bc46d..1c7dbbf9e449 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1070,6 +1070,17 @@ config FAIL_IO_TIMEOUT
           Only works with drivers that use the generic timeout handling,
           for others it wont do anything.
 
+config FAIL_MMC_REQUEST
+        bool "Fault-injection capability for MMC IO"
+        select DEBUG_FS
+        depends on FAULT_INJECTION && MMC
+        help
+          Provide fault-injection capability for MMC IO.
+          This will make the mmc core return data errors. This is
+          useful to test the error handling in the mmc block device
+          and to test how the mmc host driver handles retries from
+          the block device.
+
 config FAULT_INJECTION_DEBUG_FS
         bool "Debugfs entries for fault-injection capabilities"
         depends on FAULT_INJECTION && SYSFS && DEBUG_FS