On Sat, 21 May 2022 06:44:41 +0000 Christophe Leroy wrote: > > Hm, I think the patch is necessary, sorry if you're also saying that > > and I'm misinterpreting. > > Well, I say the contrary. > > On the mainline the patch may be applied as is, it won't harm. > > However, it is gets applied to kernel 4.9 (based on the fixes: tag), it > will break the driver for at least powerpc 8xx.
I see, we should make a note of that in the commit message so it doesn't get sucked into stable. > > Without the dma_sync_single_for_cpu() if swiotlb is used the data > > will not be copied back into the original buffer if there is no sync. > > I don't know how SWIOTLB works or even what it is, does any of the > microcontrollers embedding freescale ethernet uses that at all ? AFAIU SWIOTLB basically forces the use of bounce buffers even if the device can reach the entire DRAM. I think some people also use it for added security? IDK. I mostly use it to check if I'm using the DMA API "right" :)
