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Noralf Trønnes 9aaabaaf4a i2c: bcm2835: Add debug support
This adds a debug module parameter to aid in debugging transfer issues
by printing info to the kernel log. When enabled, status values are
collected in the interrupt routine and msg info in
bcm2835_i2c_start_transfer(). This is done in a way that tries to avoid
affecting timing. Having printk in the isr can mask issues.

debug values (additive):
1: Print info on error
2: Print info on all transfers
3: Print messages before transfer is started

The value can be changed at runtime:
/sys/module/i2c_bcm2835/parameters/debug

Example output, debug=3:
[  747.114448] bcm2835_i2c_xfer: msg(1/2) write addr=0x54, len=2 flags= [i2c1]
[  747.114463] bcm2835_i2c_xfer: msg(2/2) read addr=0x54, len=32 flags= [i2c1]
[  747.117809] start_transfer: msg(1/2) write addr=0x54, len=2 flags= [i2c1]
[  747.117825] isr: remain=2, status=0x30000055 : TA TXW TXD TXE  [i2c1]
[  747.117839] start_transfer: msg(2/2) read addr=0x54, len=32 flags= [i2c1]
[  747.117849] isr: remain=32, status=0xd0000039 : TA RXR TXD RXD  [i2c1]
[  747.117861] isr: remain=20, status=0xd0000039 : TA RXR TXD RXD  [i2c1]
[  747.117870] isr: remain=8, status=0x32 : DONE TXD RXD  [i2c1]

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
2025-12-01 12:27:28 +00:00
2025-12-01 12:27:28 +00:00
2025-12-01 12:27:28 +00:00
2022-09-28 09:02:20 +02:00
2025-02-19 14:53:27 -07:00
2025-11-30 14:42:10 -08:00
2024-03-18 03:36:32 -06:00

Linux kernel

There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first.

In order to build the documentation, use make htmldocs or make pdfdocs. The formatted documentation can also be read online at:

https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.

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