[U-Boot] [RFC PATCH 1/1] Read mmc device memory capacity from EXT_CSD if memory is addressed by sector

[Frank Bormann]

Hello Everyone,

I believe, there is a bug in the mmc driver code pertaining to how u-boot 
detects memory size of an mmc device. However, I am not 100% sure, my solution 
conforms to the JEDEC standard. So I am putting it up for discussion.

Previously, sector count indicated by mmc devices in the EXT_CSD
would only be used in u-boot if the size indicated is greater than
2 GB. This seems to be incorrect. I am working with a 4 GB Micron
eMMC device that after partition configuration and setting the
user data area to enhanced mode has a remaining capacity of less
than 2 GB for the user data area. JESD84-B50 explicitly states in
6.2.4 that for these devices SEC_CNT from the EXT_CSD is still
valid even if the memory size for that device has dropped below
2 GB by the partition configuration applied. The access mode bits
from the OCR register seem to provide a better way to decide
whether to use the CSD-based C_SIZE & C_MULT or the EXT_CSD-based
SEC_CNT information when determining the device's capacity.

In particular, this fixes a bug where u-boot SPL would assign 0 to
mmc->block_dev.lba later on in the mmc_startup() function and
subsequently fail to load u-boot from that mmc due to the original
C_SIZE & C_MULT code assigning a 4 TB size to mmc->capacity, that
incorrect capacity never being overwritten by the SEC_CNT capacity
calculation (due to its size being less than 2 GB) and then finally
lldiv(mmc->capacity, mmc->read_bl_len) exceeding the 32-bit result
data type of mmc->block_dev.lba.

Signed-off-by: Frank Bormann <fbormann at yahoo.com>
---
  drivers/mmc/mmc.c |   10 +++++-----
  include/mmc.h     |    1 +
  2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index c6a1c23..c5d1efc 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -935,19 +935,19 @@ static int mmc_startup(struct mmc *mmc)
         if (!IS_SD(mmc) && (mmc->version >= MMC_VERSION_4)) {
                 /* check  ext_csd version and capacity */
                 err = mmc_send_ext_csd(mmc, ext_csd);
-               if (!err && (ext_csd[EXT_CSD_REV] >= 2)) {
+               if (!err && (ext_csd[EXT_CSD_REV] >= 2) &&
+                       (mmc->ocr & OCR_ACCESS_MODE) == OCR_ACCESS_BY_SECTOR) {
                         /*
                          * According to the JEDEC Standard, the value of
-                        * ext_csd's capacity is valid if the value is more
-                        * than 2GB
+                        * ext_csd's capacity is valid if the device addresses
+                        * its memory by sector
                          */
                         capacity = ext_csd[EXT_CSD_SEC_CNT] << 0
                                         | ext_csd[EXT_CSD_SEC_CNT + 1] << 8
                                         | ext_csd[EXT_CSD_SEC_CNT + 2] << 16
                                         | ext_csd[EXT_CSD_SEC_CNT + 3] << 24;
                         capacity *= MMC_MAX_BLOCK_LEN;
-                       if ((capacity >> 20) > 2 * 1024)
-                               mmc->capacity_user = capacity;
+                       mmc->capacity_user = capacity;
                 }

                 switch (ext_csd[EXT_CSD_REV]) {
diff --git a/include/mmc.h b/include/mmc.h
index e1060b9..816b580 100644
--- a/include/mmc.h
+++ b/include/mmc.h
@@ -104,6 +104,7 @@
  #define OCR_HCS                        0x40000000
  #define OCR_VOLTAGE_MASK       0x007FFF80
  #define OCR_ACCESS_MODE                0x60000000
+#define OCR_ACCESS_BY_SECTOR   (1 << 30)

  #define SECURE_ERASE           0x80000000