[U-Boot] [RFC] mmc: Properly determine maximum supported bus width

[Andy Fleming]

At some point, a confusion arose about the use of the bit
definitions in host_caps for bus widths, and the value
in ext_csd. By coincidence, a simple shift could convert
between one and the other:

MMC_MODE_1BIT = 0, EXT_CSD_BUS_WIDTH_1 = 0
MMC_MODE_4BIT = 0x100, EXT_CSD_BUS_WIDTH_4 = 1
MMC_MODE_8BIT = 0x200, EXT_CSD_BUS_WIDTH_8 = 2

However, as host_caps is a bitmask of supported things,
there is not, in fact, a one-to-one correspondence. host_caps
is capable of containing MODE_4BIT | MODE_8BIT, so nonsensical
things were happening where we would try to set the bus width
to 12.

The new code clarifies the very different namespaces:

host_caps/card_caps = bitmask (MMC_MODE_*)
ext CSD fields are just an index (EXT_CSD_BUS_WIDTH_*)
mmc->bus_width integer number of bits (1, 4, 8)

We create arrays to map between the namespaces, like in Linux.

Signed-off-by: Andy Fleming <afleming at freescale.com>
---

This is, I think, the approach we should use to identify the
proper bus width for an mmc device. Please review and/or test.


 drivers/mmc/mmc.c |   47 +++++++++++++++++++++++++++++++++++------------
 1 file changed, 35 insertions(+), 12 deletions(-)

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 5fbf956..c379a74 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -867,7 +867,7 @@ void mmc_set_bus_width(struct mmc *mmc, uint width)
 
 int mmc_startup(struct mmc *mmc)
 {
-	int err, width;
+	int err;
 	uint mult, freq;
 	u64 cmult, csize, capacity;
 	struct mmc_cmd cmd;
@@ -1086,21 +1086,44 @@ int mmc_startup(struct mmc *mmc)
 		else
 			mmc->tran_speed = 25000000;
 	} else {
-		width = ((mmc->host_caps & MMC_MODE_MASK_WIDTH_BITS) >>
-			 MMC_MODE_WIDTH_BITS_SHIFT);
-		for (; width >= 0; width--) {
-			/* Set the card to use 4 bit*/
+		int idx;
+
+		/* An array of possible bus widths in order of preference */
+		static unsigned ext_csd_bits[] = {
+			EXT_CSD_BUS_WIDTH_8,
+			EXT_CSD_BUS_WIDTH_4,
+			EXT_CSD_BUS_WIDTH_1,
+		};
+
+		/* An array to map CSD bus widths to host cap bits */
+		static unsigned ext_to_hostcaps[] = {
+			[EXT_CSD_BUS_WIDTH_4] = MMC_MODE_4BIT,
+			[EXT_CSD_BUS_WIDTH_8] = MMC_MODE_8BIT,
+		};
+
+		/* An array to map chosen bus width to an integer */
+		static unsigned widths[] = {
+			8, 4, 1,
+		};
+
+		for (idx=0; idx < ARRAY_SIZE(ext_csd_bits); idx++) {
+			unsigned int extw = ext_csd_bits[idx];
+
+			/*
+			 * Check to make sure the controller supports
+			 * this bus width, if it's more than 1
+			 */
+			if (extw != EXT_CSD_BUS_WIDTH_1 &&
+					!(mmc->host_caps & ext_to_hostcaps[extw]))
+				continue;
+
 			err = mmc_switch(mmc, EXT_CSD_CMD_SET_NORMAL,
-					EXT_CSD_BUS_WIDTH, width);
+					EXT_CSD_BUS_WIDTH, extw);
 
 			if (err)
 				continue;
 
-			if (!width) {
-				mmc_set_bus_width(mmc, 1);
-				break;
-			} else
-				mmc_set_bus_width(mmc, 4 * width);
+			mmc_set_bus_width(mmc, widths[idx]);
 
 			err = mmc_send_ext_csd(mmc, test_csd);
 			if (!err && ext_csd[EXT_CSD_PARTITIONING_SUPPORT] \
@@ -1114,7 +1137,7 @@ int mmc_startup(struct mmc *mmc)
 				 && memcmp(&ext_csd[EXT_CSD_SEC_CNT], \
 					&test_csd[EXT_CSD_SEC_CNT], 4) == 0) {
 
-				mmc->card_caps |= width;
+				mmc->card_caps |= ext_to_hostcaps[extw];
 				break;
 			}
 		}
-- 
1.7.9.7