Write to physical memory from kernel module - c

Question

This question has been asked at least a dozen times but I cannot figure out where is my issue.
I am writing a kernel module that must read data from a reserved memory range. These data are written by an external device.
To control the the device, we have a second register within which I want to write some data.
And this is where I start to get lost...
This is the part of the code that, from my understanding, should create a virtual mapping from the reg input in my device tree:
// Read the control memory and map to virtual address
res_ctrl = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (!res_ctrl) {
dev_err(&pdev->dev, "can't get device resources\n");
return -ENOENT;
}
p3chvideo_device->pchv_ctrl.paddr = res_ctrl->start;
p3chvideo_device->pchv_ctrl.size = resource_size(res_ctrl);
struct resource* res_d = request_mem_region(p3chvideo_device->pchv_ctrl.paddr, p3chvideo_device->pchv_ctrl.size, "p3chv");
p3chvideo_device->pchv_ctrl.vaddr = ioremap_nocache(p3chvideo_device->pchv_ctrl.paddr, p3chvideo_device->pchv_ctrl.size);
if (!p3chvideo_device->pchv_ctrl.vaddr) {
pr_info("Control buffer allocated vaddr: 0x%0llX paddr: 0x%0llX (size: 0x%0llX)\n", p3chvideo_device->pchv_ctrl.vaddr, p3chvideo_device->pchv_ctrl.paddr, p3chvideo_device->pchv_ctrl.size);
return -EADDRNOTAVAIL;
}
//p3chvideo_device->pchv_ctrl.vaddr = devm_ioremap(&pdev->dev, p3chvideo_device->pchv_ctrl.paddr, p3chvideo_device->pchv_ctrl.size);//ioremap(p3chvideo_device->pchv_ctrl.paddr, p3chvideo_device->pchv_ctrl.size);
pr_info("Control buffer allocated vaddr: 0x%0llX paddr: 0x%0llX (size: 0x%0llX)\n", p3chvideo_device->pchv_ctrl.vaddr, p3chvideo_device->pchv_ctrl.paddr, p3chvideo_device->pchv_ctrl.size);
From the messages in the kernel, the register is correctly detected (offset, size). In addition, I do see in /proc/iomem the reserved memory.
However, when I try to write then read the results, it doesn't work, the value I read is different from the value I wrote... It is as if the register value wasn't altered by the write operation.
static void buffer_loaded_enable_interrupt(void) {
pr_info("buffer loaded enable interrupt 0x%0llX 0x%0X\n", p3chvideo_device->pchv_ctrl.vaddr + IRQ_ENABLE_BUFFER_LOADED, (u32)(1 << 0));
// Clear buffer Loaded Interrupt
//wmb();
pr_info("Stored value before: 0x%0X", readl(p3chvideo_device->pchv_ctrl.vaddr + IRQ_ENABLE_BUFFER_LOADED));
//*(p3chvideo_device->pchv_ctrl.vaddr + IRQ_ENABLE_BUFFER_LOADED) = (u32)(1 << 0);
iowrite32((u32)(1 << 0), p3chvideo_device->pchv_ctrl.vaddr + IRQ_ENABLE_BUFFER_LOADED);
udelay(100);
pr_info("Stored value: 0x%0X", readl(p3chvideo_device->pchv_ctrl.vaddr + IRQ_ENABLE_BUFFER_LOADED));
}
If I use a devmem approach, I can write ahd check the read and it works...
What am I missing?

Answer 1

I finally found the issue and I am posting it so if anyone has the same kind of problem, maybe this could help!
The problem was not in the code I put above but in the type of vaddr. It was set as a ssize_t.
ssize_t vaddr;
As soon as I set it to void __iomem *, everything worked as expected!
void __iomem *vaddr;
Let's hope this post will help someone like me :)
Thanks