Hi Geert, On 13.03.2017 at 20:57, Geert Uytterhoeven wrote: > On Mon, Mar 13, 2017 at 7:12 PM, Adrian Fiergolski > <Adrian.Fiergolski@xxxxxxx> 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. In this case, currently, what is the proper way to handle SPI controllers (spi-xilinx) without 8-bit transmission support ? -- 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
