mmc: host: sdhci: Add a variable to defer to complete requests if needed

When using the host software queue, it will trigger the next request in
irq handler without a context switch. But the sdhci_request() can not be
called in interrupt context when using host software queue for some host
drivers, due to the get_cd() ops can be sleepable.

But for some host drivers, such as Spreadtrum host driver, the card is
nonremovable, so the get_cd() ops is not sleepable, which means we can
complete the data request and trigger the next request in irq handler
to remove the context switch for the Spreadtrum host driver.

As suggested by Adrian, we should introduce a request_atomic() API to
indicate that a request can be called in interrupt context to remove
the context switch when using mmc host software queue. But this should
be done in another thread to convert the users of mmc host software queue.
Thus we can introduce a variable in struct sdhci_host to indicate that
we will always to defer to complete requests when using the host software
queue.
Suggested-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Link: https://lore.kernel.org/r/e693e7a29beb3c1922b333f4603ea81f43d5c5b1.1581478568.git.baolin.wang7@gmail.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci.c

@@ -3250,7 +3250,7 @@ static inline bool sdhci_defer_done(struct sdhci_host *host,
 {
 	struct mmc_data *data = mrq->data;
 
-	return host->pending_reset ||
+	return host->pending_reset || host->always_defer_done ||
 	       ((host->flags & SDHCI_REQ_USE_DMA) && data &&
 		data->host_cookie == COOKIE_MAPPED);
 }

drivers/mmc/host/sdhci.h

@@ -537,6 +537,7 @@ struct sdhci_host {
 	bool irq_wake_enabled;	/* IRQ wakeup is enabled */
 	bool v4_mode;		/* Host Version 4 Enable */
 	bool use_external_dma;	/* Host selects to use external DMA */
+	bool always_defer_done;	/* Always defer to complete requests */
 
 	struct mmc_request *mrqs_done[SDHCI_MAX_MRQS];	/* Requests done */
 	struct mmc_command *cmd;	/* Current command */