Hi Mark, I think, we misunderstand. Any line of spidev (or device driver in general) is called, if master, setting its bit_per_word_mask, doesn't cover 8 bits per word. Thus, in such a case, any device driver has a possibility to be registered and handle the "limited capabilities of the controller". IMHO, the problem is in the spi core itself. I will try to be more clear. 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. Regards, Adrian On 21.02.2017 at 20:08, Mark Brown wrote: > On Mon, Feb 20, 2017 at 04:35:12PM +0100, Adrian Fiergolski wrote: >> If an SPI controller doesn't support 8 bit transfers >> (master->bits_per_word_mask), it will be never registered (tested with >> spidev): >> of_register_spi_device calls spi_add_device which calls spi_setup. The last >> takes as an argument spi_device struct, which, in case of spidev, has >> bits_per_word set to 0. Thus, the spi_setup function will set it to default >> 8. Further, the same function will call __spi_validate_bits_per_word which >> will fail the whole registration for controllers not supporting 8 bit >> transfers (i.e. xilinx-spi). > This doens't make much sense, if a device driver requires a given number > of bits per word forcing a different value via device tree is not going > to result in the driver actually working. If you want to use a device > with a controller with restricted bits per word support you need to > change the device driver to support the limited capabilities of the > controller. -- 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
