SD and MMC Device Attributes

Block device 속성

이 속성은 SD 또는 MMC 장치에 연결된 block device에 정의됩니다.

Read/write 속성 `force_ro`는 물리적 write-protect switch가 꺼져 있어도 장치를 강제로 read-only로 사용하게 합니다.

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SD and MMC Block Device Attributes
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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.
        ========                ===============================================

SD/MMC card 속성

SD와 MMC device attribute는 모두 read-only입니다.

SD and MMC Device Attributes
============================

All attributes are read-only.

        ======================        ===============================================
        cid                        Card Identification 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
        ocr                         Operation Conditions Register
        dsr                        Driver Stage Register
        cmdq_en                        Command Queue enabled:

                                        1 => enabled, 0 => not enabled
        ======================        ===============================================

Erase size와 preferred erase size

`erase_size`는 erase operation의 최소 byte 크기입니다. MMC에서는 card가 보고한 erase group size입니다. Trim과 secure trim의 최소 단위는 항상 512-byte sector 하나이므로 이 값이 적용되지 않습니다. Block-addressed SD에서는 512이고 그 외 SD에서는 0입니다.

SD/MMC card는 card 전체까지 임의로 큰 영역을 지울 수 있지만, 큰 erase는 작은 chunk로 나누는 편이 좋습니다.

이유는 세 가지입니다. 단일 erase command가 다른 모든 I/O를 오래 막을 수 있고, 사용자에게 진행률을 알릴 수 있어야 하며, erase area 크기에 margin이 곱해져 timeout이 수 분까지 커질 수 있기 때문입니다.

`erase_size`는 가장 효율적인 erase 단위가 아닐 수 있으므로 `preferred_erase_size`가 큰 영역을 나눌 적절한 chunk size를 제공합니다.

MMC에서는 card가 high-capacity erase size를 지정하면 그 값을 사용하고, 아니면 card capacity에 따라 계산합니다. SD에서는 card가 지정한 allocation unit size를 사용합니다. 단위는 byte입니다.

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.

RPMB 크기 multiplier

`raw_rpmb_size_mult`는 128 KiB block의 배수입니다.

RPMB partition의 byte 크기는 `128 KiB x raw_rpmb_size_mult`로 계산합니다.

Note on raw_rpmb_size_mult:

        "raw_rpmb_size_mult" is a multiple of 128kB block.

        RPMB size in byte is calculated by using the following equation:

                RPMB partition size = 128kB x raw_rpmb_size_mult