Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Mon, 13 Mar 2017 20:57:36 +0100 | Subject | Re: [PATCH] spi: Add spi-bits-per-word binding. |
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Hi Adrian,
On Mon, Mar 13, 2017 at 7:12 PM, Adrian Fiergolski <Adrian.Fiergolski@cern.ch> wrote: > On 13.03.2017 at 18:55, Mark Brown wrote: >>> In my case, xilinx_spi_probe function (of spi-xilinx controller) sets >>> bits_per_word_mask of spi_master struct only to 16 bits support. Later, >>> xilinx_spi_probe calls of_register_spi_devices, which calls >>> of_register_spi_devices. The last one allocates an empty spi_device >>> struct and configures different options of the spi_device according to a >>> device tree. bits_per_word are not covered here (why?), thus it is left >>> 0 (value after allocation), which, by convention, means 8 bits support. >>> At the end, the same function (of_register_spi_device) calls >>> spi_add_device which finally calls spi_setup. The last call, according >>> to convention, changes bits_per_word to 8 and calls >>> __spi_validate_bits_per_word which fails, as master doesn't support 8 >>> bit transmission. This fails registration sequence of a device driver. >>> As you see, the device driver doesn't have possibility to modify >>> bits_per_word during the registration process, thus it can't provide >>> support for such limited controllers. >> I can't see any way in which it follows from the above that it's a good >> idea to try to override bits per word settings in the device tree, that >> just wastes user time and is an abstraction failure. We need better >> handling of defaults done purely in the kernel. > If enforcing by device tree specific for a given device driver SPI_CPHA, > SPIC_CPOL, SPI_CS_HIGH, max_speed_hz, etc. if fine form the abstraction > point of view, why it doesn't apply to bits_per_word ?
Because unlike polarity, phase, and speed, bits_per_word is a property of the communication protocol.
E.g. you can talk to the same EEPROM using different polarities, phase, or speed, but bits_per_word is fixed.
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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