On 8/14/19 5:01 PM, FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu) wrote: >> Hi all, >> >> I am trying to use a tcan4550 together with a Raspberry PI 3 B. I am using >> the >> tcan4x5x driver from net-next. >> I always get the following error during startup. >> tcan4x5x spi0.0: Probe failed, err=-22 >> tcan4x5x: probe of spi0.0 failed with error -22 >> >> I realized that this happens because the Raspberry PI does only support 8/9 >> bit >> words. https://elinux.org/index.php?title=RPi_SPI#Supported_bits_per_word >> In the driver it is set to 32. >> spi->bits_per_word = 32; >> >> Setting this to 8 does not help of course since the tcan chip expects a >> multiple of >> 32 per spi transaction. >> I don't know if this is a Raspberry Pi specific problem or if there are more >> devices >> with this hardware limitation. >> >> Does anyone have a workaround for that? > > It seems to be enough to just change the bits_per_word value to 8 > >> >> If this a common issue it might be a good idea to patch the driver. I will >> check if I >> can find proper a way to do so. >> >> Regards, >> Konstantin > > Now I have another really confusing problem. Anything I write to SPI is > written little endian. The tcan chip expects big endian. > Anything I read from SPI is treated as little endian but is big endian. Does > anyone know why this happens? > Is there a flag or something I can set for the SPI device/wire to fix this?
Have you changed the bits_per_word to 8? Then you read just a stream of bytes. If you tread them as an u32 they are in host order. Marc -- Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
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