On Tue, Aug 25, 2020 at 02:39:55PM +0800, Kai Heng Feng wrote: > Hi Christoph, > > > On Aug 25, 2020, at 2:23 PM, Christoph Hellwig <h...@infradead.org> wrote: > > > > On Fri, Aug 21, 2020 at 08:32:20PM +0800, Kai-Heng Feng wrote: > >> New Intel laptops with VMD cannot reach deeper power saving state, > >> renders very short battery time. > > > > So what about just disabling VMD given how bloody pointless it is? > > Hasn't anyone learned from the AHCI remapping debacle? > > > > I'm really pissed at all this pointless crap intel comes up with just > > to make life hard for absolutely no gain. Is it so hard to just leave > > a NVMe device as a standard NVMe device instead of f*^&ing everything > > up in the chipset to make OS support a pain and I/O slower than by > > doing nothing? > > From what I can see from the hardwares at my hand, VMD only enables a PCI > domain and PCI bridges behind it. > > NVMe works as a regular NVMe under those bridges. No magic remapping happens > here.
It definitively is less bad than the AHCI remapping, that is for sure. But it still requires: - a new OS driver just to mak the PCIe device show up - indirections in the irq handling - indirections in the DMA handling - hacks for ASPSM - hacks for X (there were a few more) while adding absolutely no value. Basically we have to add a large chunk of kernel code just to undo silicone/firmware Intel added to their platform to make things complicated. I mean it is their platform and if they want a "make things complicated" option that is fine, but it should not be on by default.
