I found that if I set SPI1_CS0 to be in GPIO output and drive 1 mode (in pinmux mb1 cfg file). It stays high across reboot.
But if I set it in SPI mode, it is driven low when MB1 set it to SPI mode, and it stays low until kernel starts up. I am not sure exactly when SPI1_CS0 is driven back to high by kernel, maybe when tegra-spi driver starts up.
My guest is that if I set SPI1_CS0 in SPI mode, it stays low, until tegra-spi driver configures it and drives it high.
Is there a way to let tegra-spi driver to use GPIO CS?
Regards,
Shuo