diff options
| -rw-r--r-- | drivers/spi/spi.c | 27 | ||||
| -rw-r--r-- | include/linux/spi/spi.h | 8 |
2 files changed, 33 insertions, 2 deletions
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index db08cb868652..ef37f043fd17 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -1613,14 +1613,34 @@ static int __spi_pump_transfer_message(struct spi_controller *ctlr, } } + /* + * Drivers implementation of transfer_one_message() must arrange for + * spi_finalize_current_message() to get called. Most drivers will do + * this in the calling context, but some don't. For those cases, a + * completion is used to guarantee that this function does not return + * until spi_finalize_current_message() is done accessing + * ctlr->cur_msg. + * Use of the following two flags enable to opportunistically skip the + * use of the completion since its use involves expensive spin locks. + * In case of a race with the context that calls + * spi_finalize_current_message() the completion will always be used, + * due to strict ordering of these flags using barriers. + */ + WRITE_ONCE(ctlr->cur_msg_incomplete, true); + WRITE_ONCE(ctlr->cur_msg_need_completion, false); reinit_completion(&ctlr->cur_msg_completion); + smp_wmb(); /* make these available to spi_finalize_current_message */ + ret = ctlr->transfer_one_message(ctlr, msg); if (ret) { dev_err(&ctlr->dev, "failed to transfer one message from queue\n"); return ret; } else { - wait_for_completion(&ctlr->cur_msg_completion); + WRITE_ONCE(ctlr->cur_msg_need_completion, true); + smp_mb(); /* see spi_finalize_current_message()... */ + if (READ_ONCE(ctlr->cur_msg_incomplete)) + wait_for_completion(&ctlr->cur_msg_completion); } return 0; @@ -1942,7 +1962,10 @@ void spi_finalize_current_message(struct spi_controller *ctlr) mesg->prepared = false; - complete(&ctlr->cur_msg_completion); + WRITE_ONCE(ctlr->cur_msg_incomplete, false); + smp_mb(); /* See __spi_pump_transfer_message()... */ + if (READ_ONCE(ctlr->cur_msg_need_completion)) + complete(&ctlr->cur_msg_completion); trace_spi_message_done(mesg); diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h index c56e0d240a58..eb0d316e3c36 100644 --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -385,6 +385,12 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch * @queue: message queue * @cur_msg: the currently in-flight message * @cur_msg_completion: a completion for the current in-flight message + * @cur_msg_incomplete: Flag used internally to opportunistically skip + * the @cur_msg_completion. This flag is used to check if the driver has + * already called spi_finalize_current_message(). + * @cur_msg_need_completion: Flag used internally to opportunistically skip + * the @cur_msg_completion. This flag is used to signal the context that + * is running spi_finalize_current_message() that it needs to complete() * @cur_msg_mapped: message has been mapped for DMA * @last_cs: the last chip_select that is recorded by set_cs, -1 on non chip * selected @@ -617,6 +623,8 @@ struct spi_controller { struct list_head queue; struct spi_message *cur_msg; struct completion cur_msg_completion; + bool cur_msg_incomplete; + bool cur_msg_need_completion; bool busy; bool running; bool rt; |