[PATCH 1/2] mmc: core: Add capability for 1.8V-only controllers

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From: Kyle Roeschley <kyle.roeschley@xxxxxx>

On some SD host controllers, 1.8V signaling is required for reliable
operation of the part. Add a capability which says that we must switch
to 1.8V signaling during card initialization.

Signed-off-by: Kyle Roeschley <kyle.roeschley@xxxxxx>
Signed-off-by: Jennifer Dahm <jennifer.dahm@xxxxxx>
---
 drivers/mmc/core/sd.c    | 7 +++++++
 include/linux/mmc/host.h | 1 +
 2 files changed, 8 insertions(+)

diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
index baf3d5d..b259671 100644
--- a/drivers/mmc/core/sd.c
+++ b/drivers/mmc/core/sd.c
@@ -782,6 +782,13 @@ int mmc_sd_get_cid(struct mmc_host *host, u32 ocr, u32 *cid, u32 *rocr)
 		}
 	}
 
+	if (host->caps2 & MMC_CAP2_REQUIRE_1_8V &&
+	    host->ios.signal_voltage != MMC_SIGNAL_VOLTAGE_180) {
+		pr_err("%s: Host requires UHS-capable card\n",
+		       mmc_hostname(host));
+		return -EINVAL;
+	}
+
 	err = mmc_send_cid(host, cid);
 	return err;
 }
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 8514623..4d58c10 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -354,6 +354,7 @@ struct mmc_host {
 #define MMC_CAP2_NO_MMC		(1 << 22)	/* Do not send (e)MMC commands during initialization */
 #define MMC_CAP2_CQE		(1 << 23)	/* Has eMMC command queue engine */
 #define MMC_CAP2_CQE_DCMD	(1 << 24)	/* CQE can issue a direct command */
+#define MMC_CAP2_REQUIRE_1_8V	(1 << 25)	/* Host requires 1.8V signalling */
 
 	int			fixed_drv_type;	/* fixed driver type for non-removable media */
 
-- 
2.7.4

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