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    • Mark Brown's avatar
      Merge series "TCFQ to XSPI migration for NXP DSPI driver" from Vladimir Oltean <olteanv@gmail.com> · 4a8ee2ab
      Mark Brown authored 
      Vladimir Oltean <vladimir.oltean@nxp.com>:

From: Vladimir Oltean <vladimir.oltean@nxp.com>

This series aims to remove the most inefficient transfer method from the
NXP DSPI driver.

TCFQ (Transfer Complete Flag) mode works by transferring one word,
waiting for its TX confirmation interrupt (or polling on the equivalent
status bit), sending the next word, etc, until the buffer is complete.

The issue with this mode is that it's fundamentally incompatible with
any sort of batching such as writing to a FIFO. But actually, due to
previous patchset ("Compatible string consolidation for NXP DSPI driver"):

https://patchwork.kernel.org/cover/11414593/

all existing users of TCFQ mode today already support a more advanced
feature set, in the form of XSPI (extended SPI). XSPI brings 2 extra
features:

- Word sizes up to 32 bits. This is sub-utilized today, and acceleration
  of smaller-than-32 bpw values is provided.
- "Command cycling", basically the ability to write multiple words in a
  row and receiving an interrupt only after the completion of the last
  one. This is what enables us to make use of the full FIFO depth of
  this controller.

Series was tested on the NXP LS1021A-TSN and LS1043A-RDB boards, both
functionally as well as from a performance standpoint.

The command used to benchmark the increased throughput was:

spidev_test --device /dev/spidev1.0 --bpw 8 --size 256 --cpha --iter 10000000 --speed 20000000

where spidev1.0 is a dummy spidev node, using a chip select that no
peripheral responds to.

On LS1021A, which has a 4-entry-deep FIFO and a less powerful CPU, the
performance increase brought by this patchset is from 2700 kbps to 5800
kbps.

On LS1043A, which has a 16-entry-deep FIFO and a more powerful CPU, the
performance increases from 4100 kbps to 13700 kbps.

On average, SPI software timestamping is not adversely affected by the
extra batching, due to the extra patches.

There is one extra patch which clarifies why the TCFQ users were not
converted to the "other" mode in this driver that makes use of the FIFO,
which would be EOQ mode.

My request to the many people on CC (known users and/or contributors) is
to give this series a test to ensure there are no regressions, and for
the Coldfire maintainers to clarify whether the EOQ limitation is
acceptable for them in the long run.

Vladimir Oltean (12):
  spi: spi-fsl-dspi: Simplify bytes_per_word gymnastics
  spi: spi-fsl-dspi: Remove unused chip->void_write_data
  spi: spi-fsl-dspi: Don't mask off undefined bits
  spi: spi-fsl-dspi: Add comments around dspi_pop_tx and dspi_push_rx
    functions
  spi: spi-fsl-dspi: Rename fifo_{read,write} and {tx,cmd}_fifo_write
  spi: spi-fsl-dspi: Implement .max_message_size method for EOQ mode
  spi: Do spi_take_timestamp_pre for as many times as necessary
  spi: spi-fsl-dspi: Convert TCFQ users to XSPI FIFO mode
  spi: spi-fsl-dspi: Accelerate transfers using larger word size if
    possible
  spi: spi-fsl-dspi: Optimize dspi_setup_accel for lowest interrupt
    count
  spi: spi-fsl-dspi: Use EOQ for last word in buffer even for XSPI mode
  spi: spi-fsl-dspi: Take software timestamp in dspi_fifo_write

 drivers/spi/spi-fsl-dspi.c | 421 ++++++++++++++++++++++++-------------
 drivers/spi/spi.c          |  19 +-
 include/linux/spi/spi.h    |   3 +-
 3 files changed, 288 insertions(+), 155 deletions(-)

--
2.17.1
      4a8ee2ab
    • Johan Jonker's avatar
      dt-bindings: spi: spi-rockchip: add description for rk3328 · 6ac12131
      Johan Jonker authored 
      The description below is already in use for rk3328.dtsi,
but was somehow never added to a document, so add
"rockchip,rk3328-spi", "rockchip,rk3066-spi"
for spi nodes on a rk3328 platform to spi-rockchip.yaml.
Signed-off-by: default avatarJohan Jonker <jbx6244@gmail.com>
Acked-by: default avatarRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200304184203.9548-3-jbx6244@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      6ac12131
    • Johan Jonker's avatar
      dt-bindings: spi: spi-rockchip: add description for rk3308 · db7dd939
      Johan Jonker authored 
      The description below is already in use for rk3308.dtsi,
but was somehow never added to a document, so add
"rockchip,rk3308-spi", "rockchip,rk3066-spi"
for spi nodes on a rk3308 platform to spi-rockchip.yaml.
Signed-off-by: default avatarJohan Jonker <jbx6244@gmail.com>
Acked-by: default avatarRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200304184203.9548-2-jbx6244@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      db7dd939
    • Johan Jonker's avatar
      dt-bindings: spi: convert rockchip spi bindings to yaml · 5de04175
      Johan Jonker authored 
      Current dts files with 'spi' nodes are manually verified.
In order to automate this process spi-rockchip.txt
has to be converted to yaml. In the new setup
spi-rockchip.yaml will inherit properties from
spi-controller.yaml.

Add document to MAINTAINERS.

Also rk3188.dtsi, rk3288.dtsi, rk3368.dtsi and rk3399.dtsi
use an extra fallback string, so change this in the documentation.

Changed:
"rockchip,rk3188-spi", "rockchip,rk3066-spi"
"rockchip,rk3288-spi", "rockchip,rk3066-spi"
"rockchip,rk3368-spi", "rockchip,rk3066-spi"
"rockchip,rk3399-spi", "rockchip,rk3066-spi"
Signed-off-by: default avatarJohan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20200304184203.9548-1-jbx6244@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      5de04175
    • Sascha Hauer's avatar
      spi: spi-fsl-dspi: Make bus-num property optional · 29d2daf2
      Sascha Hauer authored 
      The SPI bus number is completely optional to Linux, so make the
corresponding device tree property optional as well.
Signed-off-by: default avatarSascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20200305115546.31814-1-s.hauer@pengutronix.deSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      29d2daf2
    • Adam Ford's avatar
      spi: spi-nxp-fspi: Add support for imx8mm, imx8qxp · c7a1a20e
      Adam Ford authored 
      Add support for nxp,imx8qxp-fspi and nxp,imx8mm-fspi do the bindings
document.
Signed-off-by: default avatarAdam Ford <aford173@gmail.com>

Link: https://lore.kernel.org/r/20200126140913.2139260-4-aford173@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      c7a1a20e
    • Han Xu's avatar
      spi: spi-nxp-fspi: Enable the Octal Mode in MCR0 · b7461fa5
      Han Xu authored 
      Apply patch from NXP upstream repo to
Enable the octal combination mode in MCR0
Signed-off-by: default avatarAdam Ford <aford173@gmail.com>
Signed-off-by: default avatarHan Xu <han.xu@nxp.com>

Link: https://lore.kernel.org/r/20200126140913.2139260-3-aford173@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      b7461fa5
    • Han Xu's avatar
      spi: fspi: dynamically alloc AHB memory · d166a735
      Han Xu authored 
      Apply patch from NXP upstream repo to
dynamically allocate AHB memory as needed.
Signed-off-by: default avatarAdam Ford <aford173@gmail.com>
Signed-off-by: default avatarHan Xu <han.xu@nxp.com>

Link: https://lore.kernel.org/r/20200126140913.2139260-2-aford173@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      d166a735
    • Han Xu's avatar
      spi: fspi: enable fspi on imx8qxp and imx8mm · 941be8a7
      Han Xu authored 
      Pull in this patch from NXP's upstream repo to
enable fspi on imx8qxp and imx8mm
Signed-off-by: default avatarAdam Ford <aford173@gmail.com>
Signed-off-by: default avatarHan Xu <han.xu@nxp.com>

Link: https://lore.kernel.org/r/20200126140913.2139260-1-aford173@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      941be8a7
    • Vladimir Oltean's avatar
      spi: spi-fsl-dspi: Take software timestamp in dspi_fifo_write · e9bac900
      Vladimir Oltean authored 
      Although the SPI system timestamps are supposed to reflect the moment
that the peripheral has received a word rather than the moment when the
CPU has enqueued that word to the FIFO, in practice it is easier to just
record the latter time than the former (with a smaller error).

With the recent migration of TCFQ users from poll back to interrupt mode
(this time for XSPI FIFO), it's wiser to keep the interrupt latency
outside of the measurement of the PTP system timestamp itself. If there
proves to be any constant offset that requires static compensation, that
can always be added later. So far that does not appear to be the case at
least on the LS1021A-TSN board, where testing shows that the phc2sys
offset is able to remain within +/- 200 ns even after 68 hours of
testing.
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200304220044.11193-13-olteanv@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      e9bac900
    • Vladimir Oltean's avatar
      spi: spi-fsl-dspi: Use EOQ for last word in buffer even for XSPI mode · ea93ed4c
      Vladimir Oltean authored 
      The EOQ mode has a hardware limitation in that it stops the transmission
(including the deassertion of the chip select signal) once the host CPU
requests end-of-queue for a particular word in the TX FIFO.

And XSPI mode has a limitation in that we need a separate CMD FIFO entry
for the last byte in the buffer, where the chip select signal needs to
be deasserted. It's not a functional limitation, but it's rather clunky
and the fact that we need to halt the pipeline and write a single entry
to the TX FIFO whenever a buffer ends brings the throughput down when
transmitting small buffers.

So the idea here is to use EOQ's limitation in our favor when using XSPI
mode. Stop special-casing that final word in the buffer, and just kill
the chip select signal by issuing an EOQ for that last word. Now it can
be mixed in with all the other words in the current TX FIFO train.

A small trick here is that we still keep using the XSPI-specific
signaling via the CMDTCFQ interrupt in RSER, and not enabling the EOQ
interrupt, in order to avoid hardware weirdness (potential races with
separate interrupts being raised for CMDTCFQ and EOQ for what is in fact
the end of the same transmission). That is just theoretical, but it's
good to be cautious, and the EOQ interrupt isn't needed.
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200304220044.11193-12-olteanv@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      ea93ed4c
    • Vladimir Oltean's avatar
      spi: spi-fsl-dspi: Optimize dspi_setup_accel for lowest interrupt count · 6365504d
      Vladimir Oltean authored 
      Currently, a SPI transfer that is not multiple of the highest supported
word width (e.g. 4 bytes) will be transmitted as follows (assume a
30-byte buffer transmitted through a 32-bit wide FIFO that is 32 bytes
deep):

 - First 28 bytes are sent as 7 words of 32 bits each
 - Last 2 bytes are sent as 1 word of 16 bits size

But if the dspi_setup_accel function had decided to use a lower
oper_bits_per_word value (16 instead of 32), there would have been
enough space in the TX FIFO to fit the entire buffer in one go (15 words
of 16 bits each).

What we're actually trying to avoid is mixing word sizes within the same
run with the TX FIFO, since there is an erratum surrounding this, and
invalid data might get transmitted.

So this patch adds special cases for when the remaining length of the
buffer can be sent in one go as 8-bit or 16-bit words, otherwise it
falls back to the standard logic of sending as many bytes as possible at
the highest oper_bits_per_word value possible.

The benefit is that there will be one less CMDFQ/EOQ interrupt to
service when the entire buffer is transmitted during a single go, and
that will improve the overall latency of the transfer.
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200304220044.11193-11-olteanv@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      6365504d
    • Vladimir Oltean's avatar
      spi: spi-fsl-dspi: Accelerate transfers using larger word size if possible · 6c1c26ec
      Vladimir Oltean authored 
      This patch adds logic in the driver to transmit SPI buffers that use
bits_per_word=8 with a higher bits_per_word count (multiple of 8).

Currently the following (most common) modes are implemented:
 - 8 bits_per_word on 32-bit capable controllers
 - 8 bits_per_word on 16-bit capable controllers
 - 16 bits_per_word on 32-bit capable controllers

Transfers which are not accelerated are transferred with a hardware
bits_per_word value equal to the one of the SPI transfer.

The difference from just extending bits_per_word=32 at the spi_device
driver level is that endianness is different - the SPI core wants to
treat bits_per_word=32 buffers as arrays of u32 (i.e. words in host CPU
endianness). So to preserve endianness when clumping 8x4 bits into
32-bit words, one must perform conversion between CPU and standard (big)
endianness.

All appearances (both on the wire as well as in the buffers presented to
the peripheral driver) are preserved, just that accesses to the PUSHR
and POPR registers are now more efficient, since the same number of
reads/writes can now carry more data (2x more data on TX, 4x more data
on RX).
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200304220044.11193-10-olteanv@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      6c1c26ec
    • Vladimir Oltean's avatar
      spi: spi-fsl-dspi: Convert TCFQ users to XSPI FIFO mode · d59c90a2
      Vladimir Oltean authored 
      The Transfer Complete Flag (TCF) interrupt gets raised after each write
to the TX FIFO (PUSHR) which means that it is not possible to devise a
transfer procedure that makes full utilization of the FIFO depth (4
entries on most controllers, 16 entries on some).

On the other hand, XSPI mode has a feature called "command cycling",
which allows a single TX command to be run for a pre-specified number of
TX words. When the command cycle ends, the Command Transfer Complete
Flag bit asserts and raises an interrupt. The advantage in this mode is
that the TX FIFO can be better utilized (more words can be batched at
once).

Other changes brought by this patch:
 - The dspi->rx_end variable has been removed, since now the
   dspi_fifo_write function sets up dspi->words_in_flight, so
   dspi_fifo_read knows how much to read without overrunning the RX
   buffer.
 - Stop using poll mode unconditionally for TCFQ mode, since XSPI mode
   is a little less efficient than that, and so, poll mode doesn't bring
   as many improvements for XSPI.
 - Stop relying on the hardware transfer counter (SPI_TCR_GET_TCNT) and
   instead increment the message->actual_length based on the newly
   introduced dspi->words_in_flight variable.
 - The CTARE register is now written in the hotpath instead of just at
   transfer init time, since it contains the DTCP field (transfer
   preload - the counter indicating how many txdata words will follow),
   which is a dynamic value.

Due to the fact that the Chip Select toggling setting is part of the
command written to the TX FIFO, the ending word of each buffer needs to
be sent via its own TX command, so that we have a chance to emit a
1-word command with deasserted PCS.
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200304220044.11193-9-olteanv@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      d59c90a2
    • Vladimir Oltean's avatar
      spi: Do spi_take_timestamp_pre for as many times as necessary · 6a726824
      Vladimir Oltean authored 
      When dealing with a SPI controller driver that is sending more than 1
byte at once (or the entire buffer at once), and the SPI peripheral
driver has requested timestamping for a byte in the middle of the
buffer, we find that spi_take_timestamp_pre never records a "pre"
timestamp.

This happens because the function currently expects to be called with
the "progress" argument >= to what the peripheral has requested to be
timestamped. But clearly there are cases when that isn't going to fly.

And since we can't change the past when we realize that the opportunity
to take a "pre" timestamp has just passed and there isn't going to be
another one, the approach taken is to keep recording the "pre" timestamp
on each call, overwriting the previously recorded one until the "post"
timestamp is also taken.
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200304220044.11193-8-olteanv@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      6a726824
    • Vladimir Oltean's avatar
      spi: spi-fsl-dspi: Implement .max_message_size method for EOQ mode · a3185c38
      Vladimir Oltean authored 
      When it gets set, End Of Queue Flag halts the DSPI controller and forces
the chip select signal to deassert.

This operating mode is not ideal, but it is used for the DSPI
instantiations where there is no other notification from the controller
that the data in the FIFO has finished transmission. So in practice, it
means that transmitting buffers larger than the FIFO size will yield
unpredictable results.

The only controller that operates in EOQ mode is MCF5441X (Coldfire). I
would say that the way EOQ is used (and documented in the reference
manual, too) on this chip is incorrect, and I would personally migrate
it to TCFQ, but that's notably worse in terms of performance (it can
only use 1 entry of the 16-deep FIFO) and if this limitation didn't
bother any Coldfire DSPI user so far, it's likely that we just need to
throw an error for larger buffers to make sure that callers are aware
their transfers are getting truncated/split.
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200304220044.11193-7-olteanv@gmail.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
      a3185c38
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