linux/drivers/mmc/core/Kconfig
Linus Walleij c3dccb74be mmc: core: Delete bounce buffer Kconfig option
This option is activated by all multiplatform configs and what
not so we almost always have it turned on, and the memory it
saves is negligible, even more so moving forward. The actual
bounce buffer only gets allocated only when used, the only
thing the ifdefs are saving is a little bit of code.

It is highly improper to have this as a Kconfig option that
get turned on by Kconfig, make this a pure runtime-thing and
let the host decide whether we use bounce buffers. We add a
new property "disable_bounce" to the host struct.

Notice that mmc_queue_calc_bouncesz() already disables the
bounce buffers if host->max_segs != 1, so any arch that has a
maximum number of segments higher than 1 will have bounce
buffers disabled.

The option CONFIG_MMC_BLOCK_BOUNCE is default y so the
majority of platforms in the kernel already have it on, and
it then gets turned off at runtime since most of these have
a host->max_segs > 1. The few exceptions that have
host->max_segs == 1 and still turn off the bounce buffering
are those that disable it in their defconfig.

Those are the following:

arch/arm/configs/colibri_pxa300_defconfig
arch/arm/configs/zeus_defconfig
- Uses MMC_PXA, drivers/mmc/host/pxamci.c
- Sets host->max_segs = NR_SG, which is 1
- This needs its bounce buffer deactivated so we set
  host->disable_bounce to true in the host driver

arch/arm/configs/davinci_all_defconfig
- Uses MMC_DAVINCI, drivers/mmc/host/davinci_mmc.c
- This driver sets host->max_segs to MAX_NR_SG, which is 16
- That means this driver anyways disabled bounce buffers
- No special action needed for this platform

arch/arm/configs/lpc32xx_defconfig
arch/arm/configs/nhk8815_defconfig
arch/arm/configs/u300_defconfig
- Uses MMC_ARMMMCI, drivers/mmc/host/mmci.[c|h]
- This driver by default sets host->max_segs to NR_SG,
  which is 128, unless a DMA engine is used, and in that case
  the number of segments are also > 1
- That means this driver already disables bounce buffers
- No special action needed for these platforms

arch/arm/configs/sama5_defconfig
- Uses MMC_SDHCI, MMC_SDHCI_PLTFM, MMC_SDHCI_OF_AT91, MMC_ATMELMCI
- Uses drivers/mmc/host/sdhci.c
- Normally sets host->max_segs to SDHCI_MAX_SEGS which is 128 and
  thus disables bounce buffers
- Sets host->max_segs to 1 if SDHCI_USE_SDMA is set
- SDHCI_USE_SDMA is only set by SDHCI on PCI adapers
- That means that for this platform bounce buffers are already
  disabled at runtime
- No special action needed for this platform

arch/blackfin/configs/CM-BF533_defconfig
arch/blackfin/configs/CM-BF537E_defconfig
- Uses MMC_SPI (a simple MMC card connected on SPI pins)
- Uses drivers/mmc/host/mmc_spi.c
- Sets host->max_segs to MMC_SPI_BLOCKSATONCE which is 128
- That means this platform already disables bounce buffers at
  runtime
- No special action needed for these platforms

arch/mips/configs/cavium_octeon_defconfig
- Uses MMC_CAVIUM_OCTEON, drivers/mmc/host/cavium.c
- Sets host->max_segs to 16 or 1
- Setting host->disable_bounce to be sure for the 1 case

arch/mips/configs/qi_lb60_defconfig
- Uses MMC_JZ4740, drivers/mmc/host/jz4740_mmc.c
- This sets host->max_segs to 128 so bounce buffers are
  already runtime disabled
- No action needed for this platform

It would be interesting to come up with a list of the platforms
that actually end up using bounce buffers. I have not been
able to infer such a list, but it occurs when
host->max_segs == 1 and the bounce buffering is not explicitly
disabled.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
2017-06-20 10:30:17 +02:00

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#
# MMC core configuration
#
config PWRSEQ_EMMC
tristate "HW reset support for eMMC"
default y
depends on OF
help
This selects Hardware reset support aka pwrseq-emmc for eMMC
devices. By default this option is set to y.
This driver can also be built as a module. If so, the module
will be called pwrseq_emmc.
config PWRSEQ_SD8787
tristate "HW reset support for SD8787 BT + Wifi module"
depends on OF && (MWIFIEX || BT_MRVL_SDIO)
help
This selects hardware reset support for the SD8787 BT + Wifi
module. By default this option is set to n.
This driver can also be built as a module. If so, the module
will be called pwrseq_sd8787.
config PWRSEQ_SIMPLE
tristate "Simple HW reset support for MMC"
default y
depends on OF
help
This selects simple hardware reset support aka pwrseq-simple for MMC
devices. By default this option is set to y.
This driver can also be built as a module. If so, the module
will be called pwrseq_simple.
config MMC_BLOCK
tristate "MMC block device driver"
depends on BLOCK
default y
help
Say Y here to enable the MMC block device driver support.
This provides a block device driver, which you can use to
mount the filesystem. Almost everyone wishing MMC support
should say Y or M here.
config MMC_BLOCK_MINORS
int "Number of minors per block device"
depends on MMC_BLOCK
range 4 256
default 8
help
Number of minors per block device. One is needed for every
partition on the disk (plus one for the whole disk).
Number of total MMC minors available is 256, so your number
of supported block devices will be limited to 256 divided
by this number.
Default is 8 to be backwards compatible with previous
hardwired device numbering.
If unsure, say 8 here.
config SDIO_UART
tristate "SDIO UART/GPS class support"
depends on TTY
help
SDIO function driver for SDIO cards that implements the UART
class, as well as the GPS class which appears like a UART.
config MMC_TEST
tristate "MMC host test driver"
help
Development driver that performs a series of reads and writes
to a memory card in order to expose certain well known bugs
in host controllers. The tests are executed by writing to the
"test" file in debugfs under each card. Note that whatever is
on your card will be overwritten by these tests.
This driver is only of interest to those developing or
testing a host driver. Most people should say N here.