Conditions per spi_transfer are:
* transfer.len >= 96 bytes (to avoid mapping overhead costs)
* transfer.len < 65536 bytes (limitaion by spi-hw block - could get extended)
* an individual scatter/gather transfer length must be a multiple of 4
  for anything but the last transfer - spi-hw block limit.
  (some shortcut has been taken in can_dma to avoid unnecessary mapping of
   pages which, for which there is a chance that there is a split with a
   transfer length not a multiple of 4)

If it becomes a necessity these restrictions can get removed by additional
code.

Note that this patch requires a patch to dma-bcm2835.c by Noralf to
enable scatter-gather mode inside the dmaengine, which has not been
merged yet.

That is why no patch to arch/arm/boot/dts/bcm2835.dtsi is included - the
code works as before without dma when tx/rx are not set, but it writes
a message warning about dma not used:
spi-bcm2835 20204000.spi: no tx-dma configuration found - not using dma mode

To enable dma-mode add the following lines to the device-tree:
        dmas = <&dma 6>, <&dma 7>;
        dma-names = "tx", "rx";

Tested-by: Noralf Trønnes <noralf@tronnes.org> (private communication)
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

The polling mode of the driver is designed for transfers that run
less than 30us - it will only execute under those circumstances.
So it should run comfortably without getting interrupted by the
scheduler.

But there are situations where the raspberry pi is so overloaded
that it can take up to 80 jiffies until the polling thread gets
rescheduled - this has been observed especially under heavy
IO situations.

In such a situation we now fall back to the interrupt handler and
log the situation at debug level.
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

The way that the timeout code is written in the polling function
the timeout does also trigger when interrupted or rescheduled while
in the polling loop.

This patch changes the timeout from effectively 20ms (=2 jiffies) to
1 second and removes the time that the transfer really takes out of
the computation, as - per design - this is <30us and the jiffie resolution
is 10ms so that does not make any difference what so ever.
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

The way that the timeout code is written in the polling function
the timeout does also trigger when interrupted or rescheduled while
in the polling loop.

This patch changes the timeout from effectively 20ms (=2 jiffies) to
1 second and removes the time that the transfer really takes out of
the computation, as - per design - this is <30us and the jiffie resolution
is 10ms so that does not make any difference what so ever.
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

In cases of short transfer times the CPU is spending lots of time
in the interrupt handler and scheduler to reschedule the worker thread.

Measurements show that we have times where it takes 29.32us to between
the last clock change and the time that the worker-thread is running again
returning from wait_for_completion_timeout().

During this time the interrupt-handler is running calling complete()
and then also the scheduler is rescheduling the worker thread.

This time can vary depending on how much of the code is still in
CPU-caches, when there is a burst of spi transfers the subsequent delays
are in the order of 25us, so the value of 30us seems reasonable.

With polling the whole transfer of 4 bytes at 10MHz finishes after 6.16us
(CS down to up) with the real transfer (clock running) taking 3.56us.
So the efficiency has much improved and is also freeing CPU cycles,
reducing interrupts and context switches.

Because of the above 30us seems to be a reasonable limit for polling.
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

Transforms the bcm-2835 native SPI-chip select to their gpio-cs equivalent.

This allows for some support of some optimizations that are not
possible due to HW-gliches on the CS line - especially filling
the FIFO before enabling SPI interrupts (by writing to CS register)
while the transfer is already in progress (See commit: e3a2be30)

This patch also works arround some issues in bcm2835-pinctrl which does not
set the value when setting the GPIO as output - it just sets up output and
(typically) leaves the GPIO as low.  When a fix for this is merged then this
gpio_set_value can get removed from bcm2835_spi_setup.
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

To reduce the number of interrupts/message we fill the FIFO before
enabling interrupts - for short messages this reduces the interrupt count
from 2 to 1 interrupt.

There have been rare cases where short (<200ns) chip-select switches with
native CS have been observed during such operation, this is why this
optimization is only enabled for GPIO-CS.
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Tested-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Tested-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

This also allows for GPIO-CS to get used removing the limitation of
2/3 SPI devises on the SPI bus.

Fixes: spi-cs-high with native CS with multiple devices on the spi-bus
resetting the chip selects to "normal" polarity after a finished
transfer.

No other functionality/improvements added.

Tested with the following 4 devices on the spi-bus:
* mcp2515 with native CS
* mcp2515 with gpio CS
* fb_st7735r with native CS
    (plus spi-cs-high via transistor inverting polarity)
* enc28j60 with gpio-CS
Tested-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

The official documentation is wrong in this respect.
Has been tested empirically for dividers 2-1024
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

Implement the recommendation from the BCM2835 data-sheet
with regards to polling drivers to fill/drain the FIFO as much data as possible
also for the interrupt-driven case (which this driver is making use of).

This means that for long transfers (>64bytes) we need one interrupt
every 64 bytes instead of every 12 bytes, as the FIFO is 16 words (not bytes) wide.

Tested with mcp251x (can bus), fb_st7735 (TFT framebuffer device)
and enc28j60 (ethernet) drivers.
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

The following errors/warnings issued by checkpatch.pl --strict have been fixed:
drivers/spi/spi-bcm2835.c:182: CHECK: Alignment should match open parenthesis
drivers/spi/spi-bcm2835.c:191: CHECK: braces {} should be used on all arms of this statement
drivers/spi/spi-bcm2835.c:234: CHECK: Alignment should match open parenthesis
drivers/spi/spi-bcm2835.c:256: CHECK: Alignment should match open parenthesis
drivers/spi/spi-bcm2835.c:271: CHECK: Alignment should match open parenthesis
drivers/spi/spi-bcm2835.c:346: CHECK: Alignment should match open parenthesis
total: 0 errors, 0 warnings, 6 checks, 403 lines checked

In 2 locations the arguments had to get split/moved to the next line so that the
line width stays below 80 chars.
Signed-off-by: NMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

Signed-off-by: NJarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: NMark Brown <broonie@kernel.org>

A platform_driver does not need to set an owner, it will be populated by the
driver core.
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>

The purpose of commit 1e8a52e1
"spi: By default setup spi_masters with 1 chipselect and dynamics bus number"
is to avoid setting default value for bus_num and num_chipselect in spi master
drivers. So let's remove the duplicate code.
Signed-off-by: NAxel Lin <axel.lin@ingics.com>
Acked-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-By: NDavid Daney <david.daney@cavium.com>
Acked-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

Use devm_request_irq() to make cleanup paths simpler.
Signed-off-by: NJingoo Han <jg1.han@samsung.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

Once a spi_master_get() call succeeds, we need an additional
spi_master_put() call to free the memory, otherwise we will
leak a reference to master. Fix by removing the unnecessary
spi_master_get() call.

Fixes: 247263db ('spi: bcm2835: use devm_spi_register_master()')
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NMark Brown <broonie@linaro.org>

Use this new function to make code more comprehensible, since we are
reinitialzing the completion, not initializing.

[akpm@linux-foundation.org: linux-next resyncs]
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org> (personally at LCE13)
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Use devm_spi_register_master() to make cleanup paths simpler,
and remove a duplicate put.
Signed-off-by: NJingoo Han <jg1.han@samsung.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

The call to spi_unregister_master results in device memory being freed, it must
no longer be accessed afterwards. Thus call spi_master_get() to get an extra
reference to the device and call spi_master_put() only after the last access to
device data.

Note, current code has an extra spi_master_put() call in bcm2835_spi_remove().
Thus this patch just adds an spi_master_get() to balance the reference count.
Signed-off-by: NAxel Lin <axel.lin@ingics.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

We have a SPI_BPW_MASK macro defined in spi.h, use it instead of open-coded.
Signed-off-by: NAxel Lin <axel.lin@ingics.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

devm_ioremap_resource does sanity checks on the given resource. No need to
duplicate this in the driver.
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>
Signed-off-by: NMark Brown <broonie@linaro.org>

Replace a call to deprecated devm_request_and_ioremap by devm_ioremap_resource.

Found with coccicheck and this semantic patch:
 scripts/coccinelle/api/devm_request_and_ioremap.cocci.
Signed-off-by: NLaurent Navet <laurent.navet@gmail.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

This driver only supports bits_per_word==8, so inform the SPI core of
this. Remove all the open-coded validation that's no longer needed.
Signed-off-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

The BCM2835 contains two forms of SPI master controller (one known
simply as SPI0, and the other known as the "Universal SPI Master", in
the auxilliary block) and one form of SPI slave controller. This patch
adds support for the SPI0 controller.

This driver is taken from Chris Boot's repository at
git://github.com/bootc/linux.git rpi-linear
as of commit 6de2905 "spi-bcm2708: fix printf with spurious %s".
In the first SPI-related commit there, Chris wrote:

Thanks to csoutreach / A Robinson for his driver which I used as an
inspiration. You can find his version here:
http://piface.openlx.org.uk/raspberry-pi-spi-kernel-driver-available-for

Changes made during upstreaming:
* Renamed bcm2708 to bcm2835 as per upstream naming for this SoC.
* Removed support for brcm,realtime property.
* Increased transfer timeout to 30 seconds.
* Return IRQ_NONE from the IRQ handler if no interrupt was handled.
* Disable TA (Transfer Active) and clear FIFOs on a transfer timeout.
* Wrote device tree binding documentation.
* Request unnamed clock rather than "sys_pclk"; the DT will provide the
  correct clock.
* Assume that tfr->speed_hz and tfr->bits_per_word are always set in
  bcm2835_spi_start_transfer(), bcm2835_spi_transfer_one(), so no need
  to check spi->speed_hz or tft->bits_per_word.
* Re-ordered probe() to remove the need for temporary variables.
* Call clk_disable_unprepare() rather than just clk_unprepare() on probe()
  failure.
* Don't use devm_request_irq(), to ensure that the IRQ doesn't fire after
  we've torn down the device, but not unhooked the IRQ.
* Moved probe()'s call to clk_prepare_enable() so we can be sure the clock
  is enabled if the IRQ handler fires immediately.
* Remove redundant checks from bcm2835_spi_check_transfer() and
  bcm2835_spi_setup().
* Re-ordered IRQ handler to check for RXR before DONE. Added comments to
  ISR.
* Removed empty prepare/unprepare implementations.
* Removed use of devinit/devexit.
* Added BCM2835_ prefix to defines.
Signed-off-by: NChris Boot <bootc@bootc.net>
Signed-off-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>