about Linux_kernel:my_copy_from_user

[kojimiura]

T1024 use.

Describe below Executes from DDR memory to IFC bus connected memory (GPCM mode 16-bit width). At that time, After first writing all zeros 32 times I will write the correct value, but is it the CPU specifications?

ret=(my_copy_from_user(16,dev->mram+myctrl.off,myctrl.buff,myctrl.size));

[yipingwang]

It is required to use DMA controller to get a full burst transfer.

[kojimiura]

I have some advice.
We are continuing to investigate.
In 64-byte data copy (no burst) from DDR memory to IFC bus (GPCM mode, 16-bit width)
I checked the IFC bus chip select assertion count (CS).
① u-boot (using cp command): CS = 32 times
② Linux (using copy_from_user function): CS = 64 times
③ Linux (using memcpy function): CS = 32 times
Why does the number of CSs double when using the copy_from_user function?

[yipingwang]

pre-fetch is performed in copy_from_user