mmc: core: clarify how to use post_req in case of errors

The err condition in post_req() is set to undo a call made to pre_req()
that hasn't been started yet.  The err condition is not set if an MMC
request returns an error.

Signed-off-by: Per Forlin <per.forlin@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 45ea968e7dd..0b4c2ed22bc 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -320,8 +320,14 @@ struct mmc_async_req *mmc_start_req(struct mmc_host *host,
                 mmc_wait_for_req_done(host, host->areq->mrq);
                 err = host->areq->err_check(host->card, host->areq);
                 if (err) {
+                        /* post process the completed failed request */
                         mmc_post_req(host, host->areq->mrq, 0);
                         if (areq)
+                                /*
+                                 * Cancel the new prepared request, because
+                                 * it can't run until the failed
+                                 * request has been properly handled.
+                                 */
                                 mmc_post_req(host, areq->mrq, -EINVAL);
 
                         host->areq = NULL;