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Linux - Embedded & Single-board computer This forum is for the discussion of Linux on both embedded devices and single-board computers (such as the Raspberry Pi, BeagleBoard and PandaBoard). Discussions involving Arduino, plug computers and other micro-controller like devices are also welcome.

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Old 04-10-2012, 10:54 PM   #1
Brahmsian
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Registered: Apr 2012
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Smile Problems with dynamic registration of SPI protocol slave devices


Hi,

I am trying to write a loadable kernel module that dynamically registers a slave SPI protocol device driver on a SPI bus.

I am using the Embest SBC6000x board with AT91SAM9261S. I note that the board has two SPI buses, Bus 0 and Bus 1, and both use the SPI master controller driver in /driver/atmel_spi.c. In my case, I would like my device registered on bus 1.

The problem I encounter is that when I try to get the spi master associated with Bus 1 in the init functions of my LKM by using the spi.c function, spi_busnum_to_master(1), the function returns NULL during insmod. (i.e. no master was found associated with bus 1, spi_busnum_to_master(1) returns NULL).

How can this be? In atmel_spi.c, the master seems to be registered with the SPI framework at the end of its probe function using the spi.c function spi_register_master(). I confirmed this in my kernel init.

Everything seems to work fine if I were to use spidev instead, and statically register my spidev slave device driver during kernel startup.
 
Old 04-18-2012, 02:20 AM   #2
Brahmsian
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Registered: Apr 2012
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Solved the problem:

My arm at91 board is using the 2.6.24 kernel, and in the spi_register_master function in spi.c, you should add list_add(&master->dev.node, &spi_master_class.children); to it somewhere near the end.

list_del(&master->dev.node); should also be added to spi_unregister_master in the same file.
 
  


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