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 ? -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
