Re: spi enumeration process

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Hi Lars,

I don't think that the issue is here the two MODULE_DEVICE_TABLE modaliases in my ltc6951 driver. I have them both for the spi_device_id and also the of_device_id defined. And I believe that if any of them would be missing, then manual modprobe of the ltc6951 driver would fail too.

The issue is that it does not get automatically enumerated when my custom spi controller get loaded (i can see after boot that the spi controller is alive when looking into /proc/modules)

However, the spi slave device is not alive. The strange thing is that this does work if I connect the spi slave to the onboard SPI controller which resides inside the Zynq MPSoC.. (after putting the ltc slave in the tree under that controller)

Regards

Henk


On 10/22/21 10:25 AM, Lars-Peter Clausen wrote:
On 10/22/21 9:55 AM, Henk Medenblik wrote:
Hi all,

I am using a custom SPI controller which I created in my Xilinx MPSoC fpga part. On this custom spi controller bus I have one or more SPI devices (in my case a custom LTC6951 driver) connected in the devicetree under my spi controller. Because the controller is custom, I wrote the SPI controller driver and also some slave device drivers which seem to work.
These drivers are both created as out of tree loadable modules.

My issue is that at boot of my SocFPGA I can see that my SPI controller driver is correctly loaded during the boot process but the spi slave driver which is connected to my controller does not get automatically loaded. Therefore, I manually need to do a modprobe ltc6951.ko in my case before the LTC6951 slave in my case is up and running.

So, it seems like if I do not really understand the spi  slaves enumeration process or there is something else that I am missing here. I was under the assumption that the slaves automatically get enumerated (they are put as slaves under my controller inside the device tree) whenever it's master controller becomes alive.

Hi,

Modules are loaded by userspace, e.g. udev. It does so based on hints that are embedded in the module, these are called MODALIASs. When udev sees a device without a driver it will check all the modules to see if they have a matching modalias for the driver and then load the module.

In your driver you define the modalias usually using MODULE_DEVICE_TABLE(type, table). E.g. for a SPI driver the type would be spi and will take a reference to the spi_device_id table for your driver. In addition if you are using devicetree you do the same for the of_device_id table with `of` as the type.

- Lars




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