WANG YiFei wrote: > Hi, > > We have a board which has 1 SPI master controller and 4 SPI slave devices, > and we'd like to use 2 GPIOs to demux to chip select these slave devices. > Can anyone tell me if current powerpc dts support demuxer for chip select for > spi slave devices? So far as I know, in dts, SPI master can only use 1 to 1 > GPIO to CS(then needs 4 GPIOs).
It may be unnecessary to add other device property on the dts for your purpose. You can still get those original 2 gpios defined on the dts by default, but pass '4' to num_chipselect of your SPI master when probe SPI master. This will 'tell' kernel there are 4 kind chipselect signals for SPI sub-system. When the new SPI device is added, the kernel would acquire the number which chip should be activated by parsing chip_select of that corresponding spi_device. Then the kernel call your chipselect defined with struct spi_bitbang to set gpio. (Often we use gpio API gpio_set_value). On there you can determine how gpio_set_value() are called according to your SPI device chip_select. For example, ------ NO.0 Chip ==> gpio_set_value(PIN0, 0); gpio_set_value(PIN1, 0) NO.1 Chip ==> gpio_set_value(PIN0, 0); gpio_set_value(PIN1, 1) NO.2 Chip ==> gpio_set_value(PIN0, 1); gpio_set_value(PIN1, 0) NO.3 Chip ==> gpio_set_value(PIN0, 1); gpio_set_value(PIN1, 1) Tiejun > > > Thanks in advance, > YiFei > > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@lists.ozlabs.org > https://lists.ozlabs.org/listinfo/linuxppc-dev > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
