mmc: host: Return an error when ->enable_sdio_irq() ops is missing

Even if the current WARN() notifies the user that something is severely
wrong, we can still end up in a PANIC() when trying to invoke the missing
->enable_sdio_irq() ops. Therefore, let's also return an error code and
prevent the host from being added.

While at it, move the code into a separate function to prepare for
subsequent changes and for further host caps validations.
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20220303165142.129745-1-ulf.hansson@linaro.org

drivers/mmc/core/host.c

@@ -588,6 +588,16 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 
 EXPORT_SYMBOL(mmc_alloc_host);
 
+static int mmc_validate_host_caps(struct mmc_host *host)
+{
+	if (host->caps & MMC_CAP_SDIO_IRQ && !host->ops->enable_sdio_irq) {
+		dev_warn(host->parent, "missing ->enable_sdio_irq() ops\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 /**
  *	mmc_add_host - initialise host hardware
  *	@host: mmc host
@@ -600,8 +610,9 @@ int mmc_add_host(struct mmc_host *host)
 {
 	int err;
 
-	WARN_ON((host->caps & MMC_CAP_SDIO_IRQ) &&
-		!host->ops->enable_sdio_irq);
+	err = mmc_validate_host_caps(host);
+	if (err)
+		return err;
 
 	err = device_add(&host->class_dev);
 	if (err)