Commit f408510c authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab

docs: mmc: convert to ReST

Rename the mmc documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab+samsung@kernel.org>
parent 8ea0afa3
:orphan:
========================
MMC/SD/SDIO card support
========================
.. toctree::
:maxdepth: 1
mmc-dev-attrs
mmc-dev-parts
mmc-async-req
mmc-tools
========================
MMC Asynchronous Request
========================
Rationale Rationale
========= =========
How significant is the cache maintenance overhead? How significant is the cache maintenance overhead?
It depends. Fast eMMC and multiple cache levels with speculative cache It depends. Fast eMMC and multiple cache levels with speculative cache
pre-fetch makes the cache overhead relatively significant. If the DMA pre-fetch makes the cache overhead relatively significant. If the DMA
preparations for the next request are done in parallel with the current preparations for the next request are done in parallel with the current
transfer, the DMA preparation overhead would not affect the MMC performance. transfer, the DMA preparation overhead would not affect the MMC performance.
The intention of non-blocking (asynchronous) MMC requests is to minimize the The intention of non-blocking (asynchronous) MMC requests is to minimize the
time between when an MMC request ends and another MMC request begins. 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 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 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 possible to prepare the caches for next job in parallel with an active
...@@ -17,6 +24,7 @@ MMC block driver ...@@ -17,6 +24,7 @@ MMC block driver
================ ================
The mmc_blk_issue_rw_rq() in the MMC block driver is made non-blocking. 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 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()) 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 a request and how fast the memory is. The faster the MMC/SD is the
...@@ -35,6 +43,7 @@ MMC core API extension ...@@ -35,6 +43,7 @@ MMC core API extension
====================== ======================
There is one new public function mmc_start_req(). There is one new public function mmc_start_req().
It starts a new MMC command request for a host. The function isn't 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 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 for completion of that request and starts the new one and returns. It
...@@ -47,6 +56,7 @@ MMC host extensions ...@@ -47,6 +56,7 @@ MMC host extensions
There are two optional members in the mmc_host_ops -- pre_req() and 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 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. 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 In the DMA case pre_req() may do dma_map_sg() and prepare the DMA
descriptor, and post_req() runs the dma_unmap_sg(). descriptor, and post_req() runs the dma_unmap_sg().
...@@ -55,33 +65,34 @@ Optimize for the first request ...@@ -55,33 +65,34 @@ Optimize for the first request
The first request in a series of requests can't be prepared in parallel The first request in a series of requests can't be prepared in parallel
with the previous transfer, since there is no previous request. with the previous transfer, since there is no previous request.
The argument is_first_req in pre_req() indicates that there is no previous 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 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 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, request in two chunks, prepare the first chunk and start the request,
and finally prepare the second chunk and start the transfer. and finally prepare the second chunk and start the transfer.
Pseudocode to handle is_first_req scenario with minimal prepare overhead: Pseudocode to handle is_first_req scenario with minimal prepare overhead::
if (is_first_req && req->size > threshold) if (is_first_req && req->size > threshold)
/* start MMC transfer for the complete transfer size */ /* start MMC transfer for the complete transfer size */
mmc_start_command(MMC_CMD_TRANSFER_FULL_SIZE); mmc_start_command(MMC_CMD_TRANSFER_FULL_SIZE);
/* /*
* Begin to prepare DMA while cmd is being processed by MMC. * Begin to prepare DMA while cmd is being processed by MMC.
* The first chunk of the request should take the same time * The first chunk of the request should take the same time
* to prepare as the "MMC process command time". * to prepare as the "MMC process command time".
* If prepare time exceeds MMC cmd time * If prepare time exceeds MMC cmd time
* the transfer is delayed, guesstimate max 4k as first chunk size. * the transfer is delayed, guesstimate max 4k as first chunk size.
*/ */
prepare_1st_chunk_for_dma(req); prepare_1st_chunk_for_dma(req);
/* flush pending desc to the DMAC (dmaengine.h) */ /* flush pending desc to the DMAC (dmaengine.h) */
dma_issue_pending(req->dma_desc); dma_issue_pending(req->dma_desc);
prepare_2nd_chunk_for_dma(req); prepare_2nd_chunk_for_dma(req);
/* /*
* The second issue_pending should be called before MMC runs out * 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 * of the first chunk. If the MMC runs out of the first data chunk
* before this call, the transfer is delayed. * before this call, the transfer is delayed.
*/ */
dma_issue_pending(req->dma_desc); dma_issue_pending(req->dma_desc);
==================================
SD and MMC Block Device Attributes SD and MMC Block Device Attributes
================================== ==================================
...@@ -6,23 +7,29 @@ SD or MMC device. ...@@ -6,23 +7,29 @@ SD or MMC device.
The following attributes are read/write. The following attributes are read/write.
force_ro Enforce read-only access even if write protect switch is off. ======== ===============================================
force_ro Enforce read-only access even if write protect switch is off.
======== ===============================================
SD and MMC Device Attributes SD and MMC Device Attributes
============================ ============================
All attributes are read-only. All attributes are read-only.
====================== ===============================================
cid Card Identification Register cid Card Identification Register
csd Card Specific Data Register csd Card Specific Data Register
scr SD Card Configuration Register (SD only) scr SD Card Configuration Register (SD only)
date Manufacturing Date (from CID Register) date Manufacturing Date (from CID Register)
fwrev Firmware/Product Revision (from CID Register) (SD and MMCv1 only) fwrev Firmware/Product Revision (from CID Register)
hwrev Hardware/Product Revision (from CID Register) (SD and MMCv1 only) (SD and MMCv1 only)
hwrev Hardware/Product Revision (from CID Register)
(SD and MMCv1 only)
manfid Manufacturer ID (from CID Register) manfid Manufacturer ID (from CID Register)
name Product Name (from CID Register) name Product Name (from CID Register)
oemid OEM/Application ID (from CID Register) oemid OEM/Application ID (from CID Register)
prv Product Revision (from CID Register) (SD and MMCv4 only) prv Product Revision (from CID Register)
(SD and MMCv4 only)
serial Product Serial Number (from CID Register) serial Product Serial Number (from CID Register)
erase_size Erase group size erase_size Erase group size
preferred_erase_size Preferred erase size preferred_erase_size Preferred erase size
...@@ -30,7 +37,10 @@ All attributes are read-only. ...@@ -30,7 +37,10 @@ All attributes are read-only.
rel_sectors Reliable write sector count rel_sectors Reliable write sector count
ocr Operation Conditions Register ocr Operation Conditions Register
dsr Driver Stage Register dsr Driver Stage Register
cmdq_en Command Queue enabled: 1 => enabled, 0 => not enabled cmdq_en Command Queue enabled:
1 => enabled, 0 => not enabled
====================== ===============================================
Note on Erase Size and Preferred Erase Size: Note on Erase Size and Preferred Erase Size:
...@@ -44,14 +54,15 @@ Note on Erase Size and Preferred Erase Size: ...@@ -44,14 +54,15 @@ Note on Erase Size and Preferred Erase Size:
SD/MMC cards can erase an arbitrarily large area up to and SD/MMC cards can erase an arbitrarily large area up to and
including the whole card. When erasing a large area it may including the whole card. When erasing a large area it may
be desirable to do it in smaller chunks for three reasons: be desirable to do it in smaller chunks for three reasons:
1. A single erase command will make all other I/O on
1. A single erase command will make all other I/O on
the card wait. This is not a problem if the whole card the card wait. This is not a problem if the whole card
is being erased, but erasing one partition will make is being erased, but erasing one partition will make
I/O for another partition on the same card wait for the I/O for another partition on the same card wait for the
duration of the erase - which could be a several duration of the erase - which could be a several
minutes. minutes.
2. To be able to inform the user of erase progress. 2. To be able to inform the user of erase progress.
3. The erase timeout becomes too large to be very 3. The erase timeout becomes too large to be very
useful. Because the erase timeout contains a margin useful. Because the erase timeout contains a margin
which is multiplied by the size of the erase area, which is multiplied by the size of the erase area,
the value can end up being several minutes for large the value can end up being several minutes for large
...@@ -72,6 +83,9 @@ Note on Erase Size and Preferred Erase Size: ...@@ -72,6 +83,9 @@ Note on Erase Size and Preferred Erase Size:
"preferred_erase_size" is in bytes. "preferred_erase_size" is in bytes.
Note on raw_rpmb_size_mult: Note on raw_rpmb_size_mult:
"raw_rpmb_size_mult" is a multiple of 128kB block. "raw_rpmb_size_mult" is a multiple of 128kB block.
RPMB size in byte is calculated by using the following equation: RPMB size in byte is calculated by using the following equation:
RPMB partition size = 128kB x raw_rpmb_size_mult
RPMB partition size = 128kB x raw_rpmb_size_mult
============================
SD and MMC Device Partitions SD and MMC Device Partitions
============================ ============================
...@@ -18,18 +19,18 @@ platform, write access is disabled by default to reduce the chance of ...@@ -18,18 +19,18 @@ platform, write access is disabled by default to reduce the chance of
accidental bricking. accidental bricking.
To enable write access to /dev/mmcblkXbootY, disable the forced read-only To enable write access to /dev/mmcblkXbootY, disable the forced read-only
access with: access with::
echo 0 > /sys/block/mmcblkXbootY/force_ro echo 0 > /sys/block/mmcblkXbootY/force_ro
To re-enable read-only access: To re-enable read-only access::
echo 1 > /sys/block/mmcblkXbootY/force_ro echo 1 > /sys/block/mmcblkXbootY/force_ro
The boot partitions can also be locked read only until the next power on, The boot partitions can also be locked read only until the next power on,
with: with::
echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on 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 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 not support boot partition locking, the file will not exist. If the
......
======================
MMC tools introduction MMC tools introduction
====================== ======================
There is one MMC test tools called mmc-utils, which is maintained by Chris Ball, There is one MMC test tools called mmc-utils, which is maintained by Chris Ball,
you can find it at the below public git repository: you can find it at the below public git repository:
http://git.kernel.org/cgit/linux/kernel/git/cjb/mmc-utils.git/
http://git.kernel.org/cgit/linux/kernel/git/cjb/mmc-utils.git/
Functions Functions
========= =========
The mmc-utils tools can do the following: The mmc-utils tools can do the following:
- Print and parse extcsd data. - Print and parse extcsd data.
- Determine the eMMC writeprotect status. - Determine the eMMC writeprotect status.
- Set the eMMC writeprotect status. - Set the eMMC writeprotect status.
......
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