On Mon, Apr 3, 2023 at 5:18 PM Alvaro Karsz <alvaro.ka...@solid-run.com> wrote: > > Hi Jason, > > > > + /* Overwrite the control register with the new buffer size (in 4B > > > words) */ > > > + snet_write_ctrl(regs, buf_words); > > > + /* Use a memory barrier, this must be written before the opcode > > > register. */ > > > + wmb(); > > > > > > At least you need to use smp_wmb() but if you want to serialize MMIO > > writes you can simply use spinlocks after the removal of mmiowb > > work[1]. > > > > I'm not sure how a spinlock can help in this case. > The entire control mechanism is protected by the spinlock snet->ctrl_lock, so > multiple CPUs won't use it simultaneously. > > > Note that Documentation/memory-barriers.txt said: > > > > 1. All readX() and writeX() accesses to the same peripheral are > > ordered > > with respect to each other. This ensures that MMIO register > > accesses > > by the same CPU thread to a particular device will arrive in > > program > > order. > > > > So it will arrive to the pci subsystem in program order, but the pci > subsystem may reorder, right?
This is not what I read from the above doc. It said "to a particular device will arrive in program order". > I can just issue a read after the writes, something like: > > write_control > read_control > write op > read op > > What do you think? This should work. Thanks > > > > + /* Clear the control register - clear the error code if previous > > > control operation failed */ > > > + snet_write_ctrl(regs, 0); > > > + > > > + /* Write opcode and VQ idx */ > > > + val = opcode | (vq_idx << 16); > > > + snet_write_op(regs, val); > > > > I guess we need to serialize two writes here as well. > > Same here. > > Thanks > > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
