Messages in this thread |  | | From | Seraphime Kirkovski <> | Subject | [PATCH 0/2] spi: spidev: Introduce SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ command | Date | Tue, 9 May 2017 14:23:59 +0200 |
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Historically SPI_IOC_WR_MAX_SPEED_HZ was changing the ->max_speed_hz field of the underlying struct spi_dev, which made the effects last way after releasing one particular /dev/spidev* fd.
This changed in 9169051617df7 ("spi: spidev: Don't mangle max_speed_hz in underlying spi device") or 7 years after the introduction of SPI_IOC_WR_MAX_SPEED_HZ ! In the mean time there were userspace tools developped with the assumptions that the effects of this particular command are system-wide. [1] is a suite of two small programs for reading, writing and configuring SPI interfaces. The `spi-config -s` part was working good in our setup with old 3.x kernels. We discovered this "regression" when we tried to port our workflow to newer kernels.
I think, this change is necessary, on the one hand, because there are still a lot of longterm[2] supported kernels out there, whose users may be relying on SPI_IOC_WR_MAX_SPEED being system-wide and, on the other hand, this same command has been exhibiting a different behaviour for 3 years now, so its users may break, if 9169051617df7 is reverted in one way or another.
The semantics of the proposed command are the same as the old SPI_IOC_WR_MAX_SPEED_HZ.
[1] https://github.com/cpb-/spi-tools [2] A quick check on kernel.org shows that all 3.x with longterm support have not applied 9169051617df7
Seraphime Kirkovski (2): spi: spidev: introduce SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ command spi: spidev: document SPI_IOC_WR_DEFAULT_MAX_SPEED_HZ
Documentation/spi/spidev | 7 +++++++ drivers/spi/spidev.c | 8 ++++++-- include/uapi/linux/spi/spidev.h | 4 +++- 3 files changed, 16 insertions(+), 3 deletions(-)
-- 2.13.0.rc1
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