pon., 24 paź 2022 o 09:51 Russell King (Oracle) <linux@xxxxxxxxxxxxxxx> napisał(a): > > On Mon, Oct 24, 2022 at 08:51:02AM +0200, Marek Behún wrote: > > > Sure. In such a case the description of 380 variant (single core) > > > should remain untouched. > > > > > > We need to decide what to do with dual-CPU, i.e. Armada 385/388. How about: > > > - Don't change current behavior, i.e. perform a necessary kernel > > > configuration in "arm,pl310-cache" driver, > > > arch/arm/mach-mvebu/coherency.c + &coherencyfab:node in DT > > > - Satisfy of_dma_is_coherent() by adding `dma-coherent;` in > > > armada-385.dtsi only (IMO this would describe HW properly) > > > ? > > > > It will describe HW properly, but someone running older kernel compiled > > with no SMP support will see a performance drop. I wonder how many > > people do that. > > If the kernel is built without SMP support, the page table entries will > not have the shared bit set, and the system will _not_ be DMA-coherent. > Having DT mark devices as "dma-coherent" in this case will lead to data > corruption, because the DMA API will believe them to be DMA-coherent > when the page tables are not setup for that to work. > Thanks, for the explanation. Since we're heavily dependent on what happens in the kernel we boot, it will be easier to just drop this patch and keep using the DT as-is. Best regards, Marcin
