- 11 Sep, 2019 9 commits
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Lukas Wunner authored
The BCM2835 SPI driver currently sets the SPI_CONTROLLER_MUST_TX flag. When performing an RX-only transfer, this flag causes the SPI core to allocate and DMA-map a dummy buffer which is copied to the TX FIFO. The dummy buffer is necessary because the chip is not capable of automatically clocking out null bytes. Avoid the overhead induced by the dummy buffer by preallocating a reusable DMA transaction which fills the TX FIFO by cyclically copying from the zero page. The transaction requires very little CPU time to submit and generates no interrupts while running. Specifics are provided in kerneldoc comments. [Nathan Chancellor contributed a DMA mapping fixup for an early version of this commit, hence his Signed-off-by.] Tested-by:
Nuno Sá <nuno.sa@analog.com> Tested-by:
Noralf Trønnes <noralf@tronnes.org> Signed-off-by:
Nathan Chancellor <natechancellor@gmail.com> Signed-off-by:
Lukas Wunner <lukas@wunner.de> Acked-by:
Stefan Wahren <wahrenst@gmx.net> Acked-by:
Martin Sperl <kernel@martin.sperl.org> Cc: Robert Jarzmik <robert.jarzmik@free.fr> Link: https://lore.kernel.org/r/f45920af18dbf06e34129bbc406f53dc9c5d1075.1568187525.git.lukas@wunner.deSigned-off-by:
Mark Brown <broonie@kernel.org>
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Lukas Wunner authored
The BCM2835 SPI driver currently sets the SPI_CONTROLLER_MUST_RX flag. When performing a TX-only transfer, this flag causes the SPI core to allocate and DMA-map a dummy buffer into which the RX FIFO contents are copied. The dummy buffer is necessary because the chip is not capable of disabling the receiver or automatically throwing away received data. Not reading the RX FIFO isn't an option either since transmission is halted once it's full. Avoid the overhead induced by the dummy buffer by preallocating a reusable DMA transaction which cyclically clears the RX FIFO. The transaction requires very little CPU time to submit and generates no interrupts while running. Specifics are provided in kerneldoc comments. With a ks8851 Ethernet chip attached to the SPI controller, I am seeing a 30 us reduction in ping time with this commit (1.819 ms vs. 1.849 ms, average of 100,000 packets) as well as a 2% reduction in CPU time (75:08 vs. 76:39 for transmission of 5 GByte over the SPI bus). The commit uses the TX DMA interrupt to signal completion of a transfer. This interrupt is raised once all bytes have been written to the TX FIFO and it is then necessary to busy-wait for the TX FIFO to become empty before the transfer can be finalized. As an alternative approach, I have explored using the SPI controller's DONE interrupt to detect completion. This interrupt is signaled when the TX FIFO becomes empty, avoiding the need to busy-wait. However latency deteriorates compared to the present commit and surprisingly, CPU time is slightly higher as well: It turns out that in 45% of the cases, no busy-waiting is needed at all and in 76% of the cases, less than 10 busy-wait iterations are sufficient for the TX FIFO to drain. This was measured on an RT kernel. On a vanilla kernel, wakeup latency is worse and thus fewer iterations are needed. The measurements were made with an SPI clock of 20 MHz, they may differ slightly for slower or faster clock speeds. Previously we always used the RX DMA interrupt to signal completion of a transfer. Using the TX DMA interrupt now introduces a race condition: TX DMA is always started before RX DMA so that bytes are already clocked out while RX DMA is still being set up. But if a TX-only transfer is very short, then the TX DMA interrupt may occur before RX DMA is set up. If the interrupt happens to occur on the same CPU, setup of RX DMA may even be delayed until after the interrupt was handled. I've solved this by having the TX DMA callback clear the RX FIFO while busy-waiting for the TX FIFO to drain, thus avoiding a dependency on setup of RX DMA. Additionally, I am using a lock-free mechanism with two flags, tx_dma_active and rx_dma_active plus memory barriers to terminate RX DMA either by the TX DMA callback or immediately after setting it up, whichever wins the race. I've explored an alternative approach which temporarily disables the TX DMA callback until RX DMA has been set up (using tasklet_disable(), local_bh_disable() or local_irq_save()), but the performance was minimally worse. [Nathan Chancellor contributed a DMA mapping fixup for an early version of this commit, hence his Signed-off-by.] Tested-by:
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Lukas Wunner authored
The BCM2835 DMA controller is capable of synthesizing zeroes instead of copying them from a source address. The feature is enabled by setting the SRC_IGNORE bit in the Transfer Information field of a Control Block: "Do not perform source reads. In addition, destination writes will zero all the write strobes. This is used for fast cache fill operations." https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf The feature is only available on 8 of the 16 channels. The others are so-called "lite" channels with a limited feature set and performance. Enable the feature if a cyclic transaction copies from the zero page. This reduces traffic on the memory bus. A forthcoming use case is the BCM2835 SPI driver, which will cyclically copy from the zero page to the TX FIFO. The idea to use SRC_IGNORE was taken from an ancient GitHub conversation between Martin and Noralf: https://github.com/msperl/spi-bcm2835/issues/13#issuecomment-98180451Tested-by:
Vinod Koul <vkoul@kernel.org> Acked-by:
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Lukas Wunner authored
The BCM2835 SPI driver needs to set up the clock polarity in its ->prepare_message() hook before spi_transfer_one_message() asserts chip select to avoid a gratuitous clock signal edge (cf. commit acace73d ("spi: bcm2835: set up spi-mode before asserting cs-gpio")). Precalculate the CS register value (which selects the clock polarity) once in ->setup() and use that cached value in ->prepare_message() and ->transfer_one(). This avoids one MMIO read per message and one per transfer, yielding a small latency improvement. Additionally, a forthcoming commit will use the precalculated value to derive the register value for clearing the RX FIFO, which will eliminate the need for an RX dummy buffer when performing TX-only DMA transfers. Tested-by:
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Lukas Wunner authored
Document the BCM2835 DMA driver's device data structure so that upcoming commits may add further members with proper kerneldoc. Tested-by:
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Lukas Wunner authored
__spi_alloc_controller() uses a single allocation to accommodate struct spi_controller and the driver-private data, but places the latter behind the former. This order does not guarantee cacheline alignment of the driver-private data. (It does guarantee cacheline alignment of struct spi_controller but the structure doesn't make any use of that property.) Round up struct spi_controller to cacheline size. A forthcoming commit leverages this to grant DMA access to driver-private data of the BCM2835 SPI master. An alternative, less economical approach would be to use two allocations. A third approach consists of reversing the order to conserve memory. But Mark Brown is concerned that it may result in a performance penalty on architectures that don't like unaligned accesses. Signed-off-by:
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Lukas Wunner authored
The DMA engine API requires DMA drivers to explicitly allow that descriptors are prepared once and reused multiple times. Only a single driver makes use of this functionality so far (pxa_dma.c, to speed up pxa_camera.c). We're about to add another use case for reusable descriptors in the BCM2835 SPI driver, so allow that in the BCM2835 DMA driver. Tested-by:
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Lukas Wunner authored
The BCM2835 DMA driver currently requests an interrupt from the controller regardless whether or not the client has passed in the DMA_PREP_INTERRUPT flag. This causes unnecessary overhead for cyclic transactions which do not need an interrupt after each period. We're about to add such a use case, namely cyclic clearing of the SPI controller's RX FIFO, so amend the DMA driver to request an interrupt only if DMA_PREP_INTERRUPT was passed in. Ignore the period_len for such transactions and set it to the buffer length to make the driver's calculations work. Tested-by:
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Lukas Wunner authored
The BCM2835 SPI driver uses a flag to keep track of whether a DMA transfer is in progress. The flag is used to avoid terminating DMA channels multiple times if a transfer finishes orderly while simultaneously the SPI core invokes the ->handle_err() callback because the transfer took too long. However terminating DMA channels multiple times is perfectly fine, so the flag is unnecessary for this particular purpose. The flag is also used to avoid invoking bcm2835_spi_undo_prologue() multiple times under this race condition. However multiple *concurrent* invocations can no longer happen since commit 2527704d ("spi: bcm2835: Synchronize with callback on DMA termination") because the ->handle_err() callback now uses the _sync() variant when terminating DMA channels. The only raison d'être of the flag is therefore that bcm2835_spi_undo_prologue() cannot cope with multiple *sequential* invocations. Achieve that by setting tx_prologue to 0 at the end of the function. Subsequent invocations thus become no-ops. With that, the dma_pending flag becomes unnecessary, so drop it. Tested-by:
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- 09 Sep, 2019 1 commit
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Markus Elfring authored
Simplify this function implementation by using a known function. Generated by: scripts/coccinelle/api/ptr_ret.cocci Signed-off-by:
Markus Elfring <elfring@users.sourceforge.net> Reviewed-by:
Geert Uytterhoeven <geert+renesas@glider.be> Link: https://lore.kernel.org/r/b2dd074a-1693-3aea-42b4-da1f5ec155c4@web.deSigned-off-by:
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- 05 Sep, 2019 2 commits
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Vladimir Oltean authored
This helps a bit with line fitting now (the list_first_entry call) as well as during the next patch which needs to iterate through all transfers of ctlr->cur_msg so it timestamps them. Signed-off-by:
Vladimir Oltean <olteanv@gmail.com> Link: https://lore.kernel.org/r/20190905010114.26718-2-olteanv@gmail.comSigned-off-by:
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YueHaibing authored
drivers/spi/spi-npcm-fiu.c: In function npcm_fiu_read: drivers/spi/spi-npcm-fiu.c:472:9: warning: variable retlen set but not used [-Wunused-but-set-variable] It is never used, so remove it. Signed-off-by:
YueHaibing <yuehaibing@huawei.com> Link: https://lore.kernel.org/r/20190905072436.23932-1-yuehaibing@huawei.comSigned-off-by:
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- 04 Sep, 2019 28 commits
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
Hulk Robot <hulkci@huawei.com> Signed-off-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
Neil Armstrong <narmstrong@baylibre.com> Link: https://lore.kernel.org/r/20190904135918.25352-17-yuehaibing@huawei.comSigned-off-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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YueHaibing authored
Use devm_platform_ioremap_resource() to simplify the code a bit. This is detected by coccinelle. Reported-by:
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