BCM2835 SPI chipselect limit - kernel/driver panic

[Robert Stephens]

Bug fix was just committed by Phil Elwell <email address hidden>, and appears as response driver error reported for Raspberry Pi OS. I have the same problem with driver in Ubuntu 21.04. My apology for not knowing how driver fixes are coordinated across Pi OS and Ubuntu, so I am providing the information here in hopes a fix will be made available in Ubuntu 21.04. Please let me know if driver fix will be available for 21.04.

As background, my previous comment on github in discussion of problem with Mr. Elwell was:
A limit of 24 chipselects would work for me. -- This would likely solve problem seeing a kernel panic (bad kernel memory reference) in 5.11.0-1007-raspi after configuring 6 chipselects for for BCM2835 SPI via dtoverlay. Kernel panic is on shutdown/reboot, however, memory corruption for more than 4 chipselects likely has other runtime consequences.

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Details on new driver commit for drivers/spi/spi-bcm2835.c from Mr. Elwell on 4-30-2021:

https://github.com/raspberrypi/linux/commit/05f8d5826e28e9d82485c03b65c18d5013ba13bd

spi: bcm2835: Increase the CS limit to 24

Increase the maximum number of CS lines to 24, and ensure this limit is
not exceeded.

See: #4281 -- https://github.com/raspberrypi/linux/pull/4281

Suggested-by: Joe Burmeister <email address hidden>
Signed-off-by: Phil Elwell <email address hidden>

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