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notro / fbtft

Linux Framebuffer drivers for small TFT LCD display modules. Development has moved to https://git.kernel.org/cgit/linux/kernel/git/gregkh/staging.git/tree/drivers/staging/fbtft?h=staging-testing
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spidev2.x versus spidev1.x ? #415

Closed pdp7 closed 7 years ago

pdp7 commented 8 years ago

I'm not sure whether or not this is a fbtft issue. However, I'm not sure how to proceed at this point, and would welcome any troubleshooting advice.

I'm using Debian 8.5 (2016-08-14) image on BeagleBone Black.

I can not get fbtft working for Adafruit 1.8" LCD (ST7735R) on SPI1 when using 4.1.15-bone18 or any newer kernel packages.

However, fbtft works OK on the earlier 4.1.14-bone17 kernel.

I have noticed that: BB-SPIDEV1 cape will create /dev/spidev1.x when running 4.1.14-bone17 kernel

however: BB-SPIDEV1 cape will create /dev/spidev2.x when running 4.1.15-bone18 kernel

I have tried busnum=2 instead of busnum=1 param for fbtft_device but that did not appear to help.

Full details in this gist

notro commented 8 years ago

On face value a different bus number means a different physical SPI bus.

About numbering: spi0.1 -> bus number 0, chip select 1

Unless an alias is used, the first SPI master/bus driver in the DT gets bus number 0, the next 1 etc. Look at bus_num in http://lxr.free-electrons.com/ident?i=spi_register_master /sys/class/spi_master/ will list your SPI busses.

When the master driver is probed, it looks at the DT subnodes and adds spi devices using the reg property as the chip select value. See http://lxr.free-electrons.com/ident?i=of_register_spi_devices /sys/bus/spi/devices/ will list your SPI devices.

/proc/device-tree/ contains a filesystem representation of your active DT (if enabled).

notro commented 7 years ago

Closing issue since there has been no activity in a long time. Reopen if needed.

pdp7 commented 7 years ago

Sorry for not following up. Thanks for closing.

I believe this issue resolved by loading the SPI cape (device tree overlay) via /boot/uEnvt.txt to that it was configured correctly at boot. The issue wasn't related to anything in the fbtft code.