android_kernel_google_msm/Documentation/mmc/mmc-dev-attrs.txt

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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.
num_wr_reqs_to_start_packing This attribute is used to determine
the trigger for activating the write packing, in case the write
packing control feature is enabled.
When the MMC manages to reach a point where num_wr_reqs_to_start_packing
write requests could be packed, it enables the write packing feature.
This allows us to start the write packing only when it is beneficial
and has minimum affect on the read latency.
The number of potential packed requests that will trigger the packing
can be configured via sysfs by writing the required value to:
/sys/block/<block_dev_name>/num_wr_reqs_to_start_packing.
The default value of num_wr_reqs_to_start_packing was determined by
running parallel lmdd write and lmdd read operations and calculating
the max number of packed writes requests.
bkops_check_threshold This attribute is used to determine whether
the status bit that indicates the need for BKOPS should be checked.
The value should be given in percentages of the card size.
This value is used to calculate the minimum number of sectors that
needs to be changed in the device (written or discarded) in order to
require the status-bit of BKOPS to be checked.
The value can modified via sysfs by writing the required value to:
/sys/block/<block_dev_name>/bkops_check_threshold
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)
serial Product Serial Number (from CID Register)
erase_size Erase group size
preferred_erase_size Preferred erase size
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.
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