Check for contiguity

[balaji-ch]

Hi,

Is there a way to check that memory allocated is contagious?

For example, in Ubuntu VM (CMA enabled and disabled CONFIG_STRICT_DEVMEM)

dmesg | cma
[ 0.068544] cma: Reserved 64 MiB at 0x000000021bc00000

sudo insmod u-dma-buf.ko dma_mask_bit=64 udmabuf0=8388608
u-dma-buf udmabuf0: driver installed
u-dma-buf udmabuf0: major number   = 248
u-dma-buf udmabuf0: minor number   = 0
u-dma-buf udmabuf0: phys address   = 0x000000021be00000
u-dma-buf udmabuf0: buffer size    = 8388608
u-dma-buf udmabuf0: dma coherent  = 0

I could test this by dumping the physical memory from the ubuntu vm as sudo dd if=/dev/mem bs=1 count=8388608 skip=9057599488

But on an embedded board where I reserved the memory via DTS (instead of CMA) and when tested in the similar fashion it says dd: /dev/udmabuf0: cannot skip invalid argument

[ikwzm]

Thank you for the issue.

What kind of DTS do you use?

What arguments does the dd command specify?

[balaji-ch]

The DTS is as follows

         memory@80000000 {
            device_type = "memory";
            reg = <0x0 0x80000000 0x0 0x40000000>;

        };

        reserved-memory {
            #address-cells = <2>;
            #size-cells = <2>;
            ranges;
            image_buf0: img_buf@0xbc000000 {
                compatible = "shared-dma-pool";
                no-map;
                reg = <0x0 0xbc000000 0x0 0x4000000>;
            };

      udmabuf@0 {
        compatible = "ikwzm,u-dma-buf";
        device-name = "udmabuf0";
        size = <0x04000000>; // 64MiB
        memory-region = <&image_buf0>;

     };

The command is as follows

dd if=/dev/udmabuf0 bs=1 count=1024 skip=3154116608

[balaji-ch]

Hey I am able to resolve it by dd if=/dev/udmabuf0 bs=1 count=1024 skip=0

But when I use it like this dd if=/dev/mem bs=1 count=1024 skip=0 or dd if=/dev/mem bs=1 count=1024 skip=3154116608 I get error reading /dev/mem/ : Bad address

3154116608 is 0xbc000000

[ikwzm]

/dev/udmabuf is treated as a file of the size specified by the size property. An error will occur if you specify an area that exceeds the size.

I don't know why /dev/mem fails.