On 11/2/20 7:57 PM, Thomas.Kopp@xxxxxxxxxxxxx wrote: >> It may be a blunt guess, but according to page 99 >> >> https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm27 >> 11/rpi_DATA_2711_1p0.pdf >> >> Pin 26 is pulldown. So it works if it remains unused because the pin is >> input with pulldown thus the chip is selected by default. >> >> I don't know if the CE pin can actually work if there is no matching alt >> function in pinselect register. > Do you suggest that the communication works with a permanent low on CS/CE? No. > Without the CS/CE pin having edges you will not be able to send multiple > commands. The driver is writing/reading multiple times when bringing up the > chip. If you have a permanent low that will fail. So somehow the CS does > generate the right edges. The overlay configures the Pin for gpio and the SPI driver uses it in GPIO mode. Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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