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authorYunhong Jiang <yunhong.jiang@intel.com>2015-08-04 12:17:53 -0700
committerYunhong Jiang <yunhong.jiang@intel.com>2015-08-04 15:44:42 -0700
commit9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00 (patch)
tree1c9cafbcd35f783a87880a10f85d1a060db1a563 /kernel/Documentation/mmc
parent98260f3884f4a202f9ca5eabed40b1354c489b29 (diff)
Add the rt linux 4.1.3-rt3 as base
Import the rt linux 4.1.3-rt3 as OPNFV kvm base. It's from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-4.1.y-rt and the base is: commit 0917f823c59692d751951bf5ea699a2d1e2f26a2 Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Sat Jul 25 12:13:34 2015 +0200 Prepare v4.1.3-rt3 Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> We lose all the git history this way and it's not good. We should apply another opnfv project repo in future. Change-Id: I87543d81c9df70d99c5001fbdf646b202c19f423 Signed-off-by: Yunhong Jiang <yunhong.jiang@intel.com>
Diffstat (limited to 'kernel/Documentation/mmc')
-rw-r--r--kernel/Documentation/mmc/00-INDEX8
-rw-r--r--kernel/Documentation/mmc/mmc-async-req.txt87
-rw-r--r--kernel/Documentation/mmc/mmc-dev-attrs.txt84
-rw-r--r--kernel/Documentation/mmc/mmc-dev-parts.txt40
4 files changed, 219 insertions, 0 deletions
diff --git a/kernel/Documentation/mmc/00-INDEX b/kernel/Documentation/mmc/00-INDEX
new file mode 100644
index 000000000..a9ba6720f
--- /dev/null
+++ b/kernel/Documentation/mmc/00-INDEX
@@ -0,0 +1,8 @@
+00-INDEX
+ - this file
+mmc-dev-attrs.txt
+ - info on SD and MMC device attributes
+mmc-dev-parts.txt
+ - info on SD and MMC device partitions
+mmc-async-req.txt
+ - info on mmc asynchronous requests
diff --git a/kernel/Documentation/mmc/mmc-async-req.txt b/kernel/Documentation/mmc/mmc-async-req.txt
new file mode 100644
index 000000000..ae1907b10
--- /dev/null
+++ b/kernel/Documentation/mmc/mmc-async-req.txt
@@ -0,0 +1,87 @@
+Rationale
+=========
+
+How significant is the cache maintenance overhead?
+It depends. Fast eMMC and multiple cache levels with speculative cache
+pre-fetch makes the cache overhead relatively significant. If the DMA
+preparations for the next request are done in parallel with the current
+transfer, the DMA preparation overhead would not affect the MMC performance.
+The intention of non-blocking (asynchronous) MMC requests is to minimize the
+time between when an MMC request ends and another MMC request begins.
+Using mmc_wait_for_req(), the MMC controller is idle while dma_map_sg and
+dma_unmap_sg are processing. Using non-blocking MMC requests makes it
+possible to prepare the caches for next job in parallel with an active
+MMC request.
+
+MMC block driver
+================
+
+The mmc_blk_issue_rw_rq() in the MMC block driver is made non-blocking.
+The increase in throughput is proportional to the time it takes to
+prepare (major part of preparations are dma_map_sg() and dma_unmap_sg())
+a request and how fast the memory is. The faster the MMC/SD is the
+more significant the prepare request time becomes. Roughly the expected
+performance gain is 5% for large writes and 10% on large reads on a L2 cache
+platform. In power save mode, when clocks run on a lower frequency, the DMA
+preparation may cost even more. As long as these slower preparations are run
+in parallel with the transfer performance won't be affected.
+
+Details on measurements from IOZone and mmc_test
+================================================
+
+https://wiki.linaro.org/WorkingGroups/Kernel/Specs/StoragePerfMMC-async-req
+
+MMC core API extension
+======================
+
+There is one new public function mmc_start_req().
+It starts a new MMC command request for a host. The function isn't
+truly non-blocking. If there is an ongoing async request it waits
+for completion of that request and starts the new one and returns. It
+doesn't wait for the new request to complete. If there is no ongoing
+request it starts the new request and returns immediately.
+
+MMC host extensions
+===================
+
+There are two optional members in the mmc_host_ops -- pre_req() and
+post_req() -- that the host driver may implement in order to move work
+to before and after the actual mmc_host_ops.request() function is called.
+In the DMA case pre_req() may do dma_map_sg() and prepare the DMA
+descriptor, and post_req() runs the dma_unmap_sg().
+
+Optimize for the first request
+==============================
+
+The first request in a series of requests can't be prepared in parallel
+with the previous transfer, since there is no previous request.
+The argument is_first_req in pre_req() indicates that there is no previous
+request. The host driver may optimize for this scenario to minimize
+the performance loss. A way to optimize for this is to split the current
+request in two chunks, prepare the first chunk and start the request,
+and finally prepare the second chunk and start the transfer.
+
+Pseudocode to handle is_first_req scenario with minimal prepare overhead:
+
+if (is_first_req && req->size > threshold)
+ /* start MMC transfer for the complete transfer size */
+ mmc_start_command(MMC_CMD_TRANSFER_FULL_SIZE);
+
+ /*
+ * Begin to prepare DMA while cmd is being processed by MMC.
+ * The first chunk of the request should take the same time
+ * to prepare as the "MMC process command time".
+ * If prepare time exceeds MMC cmd time
+ * the transfer is delayed, guesstimate max 4k as first chunk size.
+ */
+ prepare_1st_chunk_for_dma(req);
+ /* flush pending desc to the DMAC (dmaengine.h) */
+ dma_issue_pending(req->dma_desc);
+
+ prepare_2nd_chunk_for_dma(req);
+ /*
+ * The second issue_pending should be called before MMC runs out
+ * of the first chunk. If the MMC runs out of the first data chunk
+ * before this call, the transfer is delayed.
+ */
+ dma_issue_pending(req->dma_desc);
diff --git a/kernel/Documentation/mmc/mmc-dev-attrs.txt b/kernel/Documentation/mmc/mmc-dev-attrs.txt
new file mode 100644
index 000000000..189bab092
--- /dev/null
+++ b/kernel/Documentation/mmc/mmc-dev-attrs.txt
@@ -0,0 +1,84 @@
+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.
+
+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
diff --git a/kernel/Documentation/mmc/mmc-dev-parts.txt b/kernel/Documentation/mmc/mmc-dev-parts.txt
new file mode 100644
index 000000000..f08d078d4
--- /dev/null
+++ b/kernel/Documentation/mmc/mmc-dev-parts.txt
@@ -0,0 +1,40 @@
+SD and MMC Device Partitions
+============================
+
+Device partitions are additional logical block devices present on the
+SD/MMC device.
+
+As of this writing, MMC boot partitions as supported and exposed as
+/dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the
+parent /dev/mmcblkX.
+
+MMC Boot Partitions
+===================
+
+Read and write access is provided to the two MMC boot partitions. Due to
+the sensitive nature of the boot partition contents, which often store
+a bootloader or bootloader configuration tables crucial to booting the
+platform, write access is disabled by default to reduce the chance of
+accidental bricking.
+
+To enable write access to /dev/mmcblkXbootY, disable the forced read-only
+access with:
+
+echo 0 > /sys/block/mmcblkXbootY/force_ro
+
+To re-enable read-only access:
+
+echo 1 > /sys/block/mmcblkXbootY/force_ro
+
+The boot partitions can also be locked read only until the next power on,
+with:
+
+echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on
+
+This is a feature of the card and not of the kernel. If the card does
+not support boot partition locking, the file will not exist. If the
+feature has been disabled on the card, the file will be read-only.
+
+The boot partitions can also be locked permanently, but this feature is
+not accessible through sysfs in order to avoid accidental or malicious
+bricking.