On 05/03/18 11:02 AM, Sinan Kaya wrote:
writel has a barrier inside on ARM64. https://elixir.bootlin.com/linux/latest/source/arch/arm64/include/asm/io.h#L143
Yes, and no barrier inside memcpy_toio as it uses __raw_writes. This should be sufficient as we are only accessing addresses that look like memory and have no side effects (those enabling doorbell accesses may need to worry about this though). Typically, what could happen, in this case, is the CPU would issue writes to the BAR normally and the next time it programmed the DMA engine it would flush everything via the flush in writel.
Why do you need another barrier?
We don't. Thanks, Logan
