Cannot write SAI register from Linux Kernel Module (IMX6ULZ)

GLavigne — Fri, 12 Feb 2021 10:15:41 GMT

Hello,

We try to write a register (SAI2 Transmit Control Register (I2S2_TCSR)) from a linux kernel module, but for some reason after trying to read the value again, it reads 0. Here is a snippet of the imx6ull.dtsi :

sai2: sai@0202c000 { compatible = "fsl,imx6ul-sai", "fsl,imx6sx-sai"; reg = <0x0202c000 0x4000>; interrupts = <GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>; clocks = <&clks IMX6UL_CLK_SAI2_IPG>, <&clks IMX6UL_CLK_DUMMY>, <&clks IMX6UL_CLK_SAI2>, <&clks 0>, <&clks 0>; clock-names = "bus", "mclk0", "mclk1", "mclk2", "mclk3"; dma-names = "rx", "tx"; dmas = <&sdma 37 24 0>, <&sdma 38 24 0>; status = "disabled"; };

And here is the dts we're adding :

&sai2 { compatible = "fsl,clock32khz_imx6ulzb2"; status = "okay"; };

Eventually, here is a part of the module :

#define I2S2_TCSR_ADDR 0x0202C000 #define I2S2_TCSR_VALUE 0xD0000000 #define SAI2_MEM_REGION_SIZE 0x200 static void *pVirtAddr_I2S2_TCSR; static int clock32khz_probe(struct platform_device *pdev) { int value; pVirtAddr_I2S2_TCSR=0; //SAI2 request mem region if(!request_mem_region(I2S2_TCSR_ADDR,SAI2_MEM_REGION_SIZE,"clock32KHz : sai2")) { printk(KERN_ERR "Failed to request mem region I2S2_TCSR_ADDR\n"); ret=-EBUSY; goto ErrSAI2req; } //I2S2_TCSR pVirtAddr_I2S2_TCSR=devm_ioremap_nocache(&pdev->dev,I2S2_TCSR_ADDR,1); if(!pVirtAddr_I2S2_TCSR) { printk(KERN_ERR "Failed to remap I/O memory I2S2_TCSR_ADDR\n"); ret=-ENXIO; goto ErrI2S2_TCSR; } value=*(int *)(pVirtAddr_I2S2_TCSR); printk(KERN_INFO "I2S2_TCSR=%X\n",value); *(int *)(pVirtAddr_I2S2_TCSR)=I2S2_TCSR_VALUE; //TEST value=*(int *)(pVirtAddr_I2S2_TCSR); printk(KERN_INFO "I2S2_TCSR test1=%X\n",value); devm_iounmap(&pdev->dev,pVirtAddr_I2S2_TCSR); pVirtAddr_I2S2_TCSR=devm_ioremap_nocache(&pdev->dev,I2S2_TCSR_ADDR,1); if(!pVirtAddr_I2S2_TCSR) { printk(KERN_ERR "Failed to remap I/O memory I2S2_TCSR_ADDR\n"); ret=-ENXIO; goto ErrI2S2_TCSR; } value=*(int *)(pVirtAddr_I2S2_TCSR); printk(KERN_INFO "I2S2_TCSR test2=%X\n",value); //TEST END //No error return 0; } static const struct of_device_id of_clock32khz_match[] = { { .compatible = "fsl,clock32khz_imx6ulzb2", }, {}, }; MODULE_DEVICE_TABLE(of, of_clock32khz_match); static struct platform_driver clock32khz_device_driver = { .probe = clock32khz_probe, .remove = clock32khz_remove, .driver = { .name = "clock32khz_imx6ulzb2", .of_match_table = of_clock32khz_match, } }; module_platform_driver(clock32khz_device_driver);

It seems that everything is working when the module is inserted, but the printk's output is :

I2S2_TCSR test1=D0000000

I2S2_TCSR test2=0

Any help would be much appreciated.

Guillaume

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