Resource Table location for remoteproc implementation in imx8mm

[pradeepas]

Hello Team,

I have been looking at the remoteproc and rpmsg Linux driver implementation for the imx8mm SoC together with the rpmsg_lite_str_echo_rtos example distributed with the SDK of cortex M4 co-processor.

In the device tree I noticed the following entries. (I only copied entries relavent to this question)

       
reserved-memory {
      vdev0vring0: vdev0vring0@b8000000 {                                                                   
            compatible = "shared-dma-pool";                                                                   
            reg = <0 0xb8000000 0 0x8000>;                                                                    
            no-map;                                                                                           
        };                                                                                                    
                                                                                                              
        vdev0vring1: vdev0vring1@b8008000 {                                                                   
            compatible = "shared-dma-pool";                                                                   
            reg = <0 0xb8008000 0 0x8000>;                                                                    
            no-map;                                                                                           
        };                                                                                                    
                                                                                                              
        rsc-table {                                                                                           
            reg = <0 0xb80ff000 0 0x1000>;                                                                    
            no-map;                                                                                           
        };                                                                                                    
}
                 
     imx8mm-cm4 {                                                                                                                                                                                                                                                               
        compatible = "fsl,imx8mm-cm4";                                                                           
        rsc-da = <0xb8000000>;                                                                                   
        clocks = <&clk IMX8MM_CLK_M4_DIV>;                                                                       
        mbox-names = "tx", "rx", "rxdb";                                                                         
        mboxes = <&mu 0 1                                                                                        
              &mu 1 1                                                                                            
              &mu 3 1>;                                                                                          
        memory-region = <&vdev0vring0>, <&vdev0vring1>, <&vdevbuffer>;                                           
        syscon = <&src>;                                                                                         
    };

When looking at the reserved-memory for m4, it seems that two vrings are placed at 0xb8000000 and 0xb008000 respectively, and the place reserved for the rsc-table is 0xb80ff000.

However, in imx8mm-cm4 node, the resource table is said to be available at 0xb8000000 location.

When looking at the SDK example rpmsg_lite_str_echo_rtos, I found the following function.

void copyResourceTable(void)
{
    /*
     * Resource table should be copied to VDEV0_VRING_BASE + RESOURCE_TABLE_OFFSET.
     * VDEV0_VRING_BASE is temperorily kept for backward compatibility, will be
     * removed in future release
     */
    memcpy((void *)VDEV0_VRING_BASE, &resources, sizeof(resources));
    memcpy((void *)(VDEV0_VRING_BASE + RESOURCE_TABLE_OFFSET), &resources, sizeof(resources));
}

It looks like we copy the resource table to both these locations (0xb8000000 and 0xb80ff000) because of probably a mistake we made in the device tree file.

I believe the first memcpy is not required if we change the device tree such that rsc-da property is 0xb80ff000. Is my understanding correct?

[AldoG]

Hello,

It is not for a mistake is for legacy compatibility of some changed features, you may refer to the following commit:
https://source.codeaurora.org/external/imx/linux-imx/commit/arch/arm64/boot/dts/freescale/imx8mn-evk...

Best regards,
Aldo.

[pradeepas]

Thank you for the response. However, I have one follow up question related to the rsc-da.

Shouldn't that property also change to have the same address as that of the rsc-table?