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SD and MMC Block Device Attributes
==================================
These attributes are defined for the block devices associated with the
SD or MMC device.
The following attributes are read/write.
force_ro Enforce read-only access even if write protect switch is off.
bouncesz Support dynamic adjustment of bounce buffer size at runtime,
from 4096 to 4194304, integer multiple of 512 bytes only.
SD and MMC Device Attributes
============================
All attributes are read-only.
cid Card Identifaction Register
csd Card Specific Data Register
scr SD Card Configuration Register (SD only)
date Manufacturing Date (from CID Register)
fwrev Firmware/Product Revision (from CID Register) (SD and MMCv1 only)
hwrev Hardware/Product Revision (from CID Register) (SD and MMCv1 only)
manfid Manufacturer ID (from CID Register)
name Product Name (from CID Register)
oemid OEM/Application ID (from CID Register)
prv Product Revision (from CID Register) (SD and MMCv4 only)
serial Product Serial Number (from CID Register)
erase_size Erase group size
preferred_erase_size Preferred erase size
raw_rpmb_size_mult RPMB partition size
rel_sectors Reliable write sector count
Note on Erase Size and Preferred Erase Size:
"erase_size" is the minimum size, in bytes, of an erase
operation. For MMC, "erase_size" is the erase group size
reported by the card. Note that "erase_size" does not apply
to trim or secure trim operations where the minimum size is
always one 512 byte sector. For SD, "erase_size" is 512
if the card is block-addressed, 0 otherwise.
SD/MMC cards can erase an arbitrarily large area up to and
including the whole card. When erasing a large area it may
be desirable to do it in smaller chunks for three reasons:
1. A single erase command will make all other I/O on
the card wait. This is not a problem if the whole card
is being erased, but erasing one partition will make
I/O for another partition on the same card wait for the
duration of the erase - which could be a several
minutes.
2. To be able to inform the user of erase progress.
3. The erase timeout becomes too large to be very
useful. Because the erase timeout contains a margin
which is multiplied by the size of the erase area,
the value can end up being several minutes for large
areas.
"erase_size" is not the most efficient unit to erase
(especially for SD where it is just one sector),
hence "preferred_erase_size" provides a good chunk
size for erasing large areas.
For MMC, "preferred_erase_size" is the high-capacity
erase size if a card specifies one, otherwise it is
based on the capacity of the card.
For SD, "preferred_erase_size" is the allocation unit
size specified by the card.
"preferred_erase_size" is in bytes.
Note on raw_rpmb_size_mult:
"raw_rpmb_size_mult" is a mutliple of 128kB block.
RPMB size in byte is calculated by using the following equation:
RPMB partition size = 128kB x raw_rpmb_size_mult
SD/MMC/SDIO Clock Gating Attribute
==================================
Read and write access is provided to following attribute.
This attribute appears only if CONFIG_MMC_CLKGATE is enabled.
clkgate_delay Tune the clock gating delay with desired value in milliseconds.
echo <desired delay> > /sys/class/mmc_host/mmcX/clkgate_delay
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