MMCSD SDIO: Add support for a new SDWAIT_WRCOMPLETE condition. The previous logic used a busy-wait loop to pool the card R1 start to determine when the card was ready for the next transfer. That busy-wait can be quite long -- hundreds of milliseconds. And alternative is to look the the SD D0 pin which will change state when the card is no longer busy.

This logic implements a change the avoids the busy-wait poll by reconfiguring the SD D0 pin as a GPIO interrupt, then waiting for the card to becom ready without taking up CPU cycles.

This change is conditioned on CONFIG_MMCSD_SDIOWATI_WRCOMPLETE and is currenlty only implemented for the STM32 SDIO driver.

From David Sidrane

drivers/mmcsd/Kconfig

@@ -38,6 +38,23 @@ config MMCSD_HAVECARDDETECT
 		SDIO driver card detection is
 		100% accurate
 
+config MMCSD_SDIOWAIT_WRCOMPLETE
+	bool "Use SDIO_D Busy to detect Write Complete"
+	default n
+	---help---
+		SDIO driver will use SDIO_D Busy signalling to detect Write Complete.
+		This option when selected, will enable the MMCSD driver to use the
+		underlying (stm32_sdio only) drivers implementation of the SD specs
+		SDIO_D Busy signalling to detect Write Complete. This will avoid
+		potentially very long (600Ms+) busy waiting in the MMCSD driver.
+
+		To implement SDIO_D Busy signalling, the underlying driver must
+		be capable of switching the GPIO_SDIO_D0 to be a rising edge sensitive
+		interrupt pin. It must then, condition that pin to detect the rising edge
+		on receipt of SDWAIT_WRCOMPLETE in the SDIO_WAITENABLE call and
+		return it back to regular SDIO mode, when either the ISR fires or pin is
+		found to be high in the SDIO_EVENTWAIT call.
+
 config MMCSD_SPI
 	bool "MMC/SD SPI transfer support"
 	default y

drivers/mmcsd/mmcsd_sdio.c

@@ -1150,6 +1150,15 @@ static int mmcsd_transferready(FAR struct mmcsd_state_s *priv)
    * the TRANSFER state when the card completes the WRITE operation.
    */
 
+#if defined(CONFIG_MMCSD_SDIOWAIT_WRCOMPLETE)
+  ret = mmcsd_eventwait(priv, SDIOWAIT_TIMEOUT|SDIOWAIT_ERROR,
+                        MMCSD_BLOCK_WDATADELAY);
+  if (ret != OK)
+    {
+      fdbg("ERROR: mmcsd_eventwait for transfer ready failed: %d\n", ret);
+    }
+#endif
+
   starttime = clock_systimer();
   do
     {
@@ -1721,6 +1730,12 @@ static ssize_t mmcsd_writesingle(FAR struct mmcsd_state_s *priv,
       return ret;
     }
 
+#if defined(CONFIG_MMCSD_SDIOWAIT_WRCOMPLETE)
+  /* Arm the write complete detection with timeout */
+
+  SDIO_WAITENABLE(priv->dev, SDIOWAIT_WRCOMPLETE|SDIOWAIT_TIMEOUT);
+#endif
+
   /* On success, return the number of blocks written */
 
   return 1;